"Apps" and "app stores" only exist to facilitate rent-seeking behavior. It's hard to make money when people don't need what you're selling... These walled gardens are not in any way an organic choice, they were foisted on the masses by big tech monopolists.
Same reason people pay others to do anything: convenience. Apps are used because most people have neither the desire nor the time to deal with manipulating data directly.
You wanna not use apps? Have fun, no one is stopping you.
Why not?
Apps (an abbreviation for the word 'Applications') are merely one subcategory of the stuff called 'Software'. We call that category 'Apps' to distinguish them from the other main category of Software, the 'Operating System'.
The operating system is a specialised piece of software for the use by any other software to interface with all the peripherals included in a machine's hardware. So, software that allows your software 'app' to use the hard drive, or display stuff on the screen, or allow you to type stuff in.
Any task undertaken on a computer involves some sort of application which runs on top of an Operating System. And that's it! There's nothing weird or wonderful about 'apps', they are merely a bunch of 'tasks' for you to do things with.