why the apps I use the most keep unistalling?!

I completely get why that’s frustrating—it’s so annoying when iOS offloads apps you use all the time! One thing that might help is going to Settings → Apps → App Store → Offload Unused Apps and turning it off, so the apps you need stay on your phone.”

Turn off “Offload Unused Apps” in Settings > Apps > App Store. You can always offload apps manually if you need to.

oleksandrayvr wrote:

I am so angry at this point. IOS keep offloading the apps that I use the most and in a lot of cases I become aware of it when I have an important work related task to do and can’t find the app I used the whole week in my phone. Meanwhile the apps I used months ago are still there. Apple devs, what does that suppose to mean?

Apple developers are not here in this user-to-user forum.

The first thing I would check is how much memory you have on your phone. Phones can start behaving erratically if they're very close to completely full.

What's the difference between device storage and iCloud storage? - Apple Support

oleksandrayvr wrote:

But did they figure out why this feature deletes the most used apps instead?

It doesn't for 99.999% of users. It is not a common problem by any means.

At least their product managers should be, that’s one of the issues everyone was asking to fix for years know apparently

It would be highly inefficient. This is one of the busiest forums of its kind in the world. And the vast majority of it would be of no interest to developers. Finding the few things that might be would be far more effort than it's worth.

The correct place for letting Apple developers know issues is the Feedback page:

Product Feedback - Apple