Learning to handstand can definitely be a journey, especially for those of us starting out as adults.
No matter your skill level or general timeline, the skill will always take longer than you think. That's one reality that you should accept.
That being said, it shouldn't take forever. If you've been at it for a while and aren't seeing the progress you want, there could be a few potential causes that are holding you back.
Being aware of your shortcomings can help you to work on your weaknesses and address your issues.

Below are 9 reasons you aren't making progress with your handstands(yet).

1. Conditioning
Handstand is a physical skill. While it's true that good technique can minimize the physical demands, conditioning will still play a vital role. You don't have to be in crazy shape, but the more fit you are the easier the skill will be to learn. It's difficult to focus on the technique if it takes tremendous effort to get into and hold yourself in the handstand position.
I personally find this portion of the practice much less interesting than the technical stuff, but if you have good conditioning it will do many favors for your practice.

2. Wrists
Many adults neglect their wrists in their practice, then later complain of wrist pain and stiffness. Handstand requires you to hold all your weight on a fairly small joint. If that's something your body isn't used to, it will take time to acclimate it. One of the best ways to do this is to perform a good wrist warmup every time you train, especially if you are new to the practice. Not only will this give you more sensitivity and awareness for balance, it will speed up the process of getting your wrists used to hand balancing. I lost count of how many times people told me how their wrists felt great during my handstand workshops after performing a thorough warm up(that they skimped on in their own training).
Check out my wrist series on vimeo: https://vimeo.com/ondemand/wristsequence

3. Inversion
Being comfortable upside down is a huge part of the handstand practice. In the case of many adults, they may not have been properly inverted since they were kids. This can be disorienting at first, so it's best to ease into it slowly to make sure you feel safe and comfortable doing it.
This is where inversions like headstands and forearm stands can be useful. They are significantly easier than a handstand due to lower center of mass and wide base of support. While they aren't direct handstand progressions, these poses allow you to spend more time upside down which will lead to more comfort and awareness.

4. Fear of Falling
Handstand is a unique skill because psychological restrictions can play as big a role as physical ones. Fear of falling forward is an important issue to address so you can be confident in your handstand. When you build the reflex to fall safely, it's much easier to fully commit to the handstand. If you are not comfortable falling forward out of a handstand, it's something you should specifically work on until it becomes second nature to you. This will open up many new degrees of freedom in your handstand practice.

5. Alignment
Holding the handstand a certain way can make it much easier to stay up there, so this is an important concept to learn. Essentially, you want to stack your joints on a vertical line which allows you to use your bone structure to hold the handstand. This decreases the physical demand of the exercise.
Unfortunately, the handstand alignment most people seek is not the most intuitive thing to learn. It takes specific training to feel the shape and be aware of the position. However, once you understand the concept it will be incredibly helpful. It doesn't have to be perfect, but paying attention to your alignment will be very beneficial.

6. Balance Focus
The balance of the handstand is a very specific sensation that is best trained specifically. Many adults assume that the balance will just happen at a certain point, but the reality is the balance is something you create. Learn to feel the weight in your hands, and how it can be manipulated through small movements in the wrist and fingers. Then learn to connect that to your entire body. Finally, learn to connect that sensation to your awareness of falling. After lots of practice, this is how you create balance.

7. Kick-up Inconsistency
What good is your handstand balance if you can't easily get there? I see many adults launch themselves into a handstand without any precision or awareness over any over without making any adjustments. Then they wonder why they can't hit the position or catch balance easily.
The kick up is something that should be trained deliberately. Get it to the point where it's smooth and consistent, then it will be much easier to balance from it.

8. Wall Reliance
The wall is a great tool for learning incremental handstand progressions, building confidence, developing balance, conditioning, etc.
However, it's also possible to become reliant on the wall to a point that it hinders your progress. Generally, I like to treat the wall as a temporary assistant. Something that you'll no longer need eventually. Try to be as light as possible when using wall assistance, and always keep in mind that the purpose of the wall is to be obsolete.
That isn't to say it's not a useful tool even for an advanced practitioner. However, the idea is to use the wall to help just the right amount, and gradually build independence from it.

9. Training Consistency
Real talk: are you actually training your handstand? Or just playing around with it occasionally? There's absolutely nothing wrong with the latter, but it probably won't get you much progress.
If you play around with handstands and inversions for a few minutes during your yoga or crossfit class, that's great! However, making long term progress will take more dedicated practice. Just something to keep in mind.

There you have it, a few ideas on why you may not be seeing the progress you want in your handstand practice. Hopefully it gives you something to think about and apply.

Check out my youtube video that talks about these points and some potential solutions.