By the way, you can not customize any shortcut, only those available in Keyboard Shortcuts dialogue. If you can not find shortcut/option to change/assign shortcut then that option/shortcut is not available to customize shortcut.
With all software that allows customization, you can only customize what the developers give you access to. The developers can only tell us the reasons if they are allowed to tell us the reasons — otherwise it is under NDA.
Yes, there are competitors. You can find them if you put "Photoshop competitors and alternatives" into a search engine.
As users, we are not privy to the reasons — or to what is in development — but we can tell you that that the number shortcuts cannot be changed. You can start a new post and tag it as "Idea" so the developers will see it. Just maybe you might see it in a future version.