Everything having a key on the keyboard

Many people agree with you and you should be able to define any symbol as a keyboard shortcut in version 3.0 if the work from last summer is incorporated when it's finally released.

Also, meanwhile, see:
https://musescore.org/en/handbook/preferences#shortcuts
where you can define a new shortcut.

Regards.

And note that in Edit / Preferences / Shortcuts, you can actually define shortcuts for quite a few commands that don't have any by default. But indeed, not everything - in particular, many palette elements cannot be added by shortcut.

BTW, I made a handy cheat sheet for the default shortcuts, it includes a few that are not well-known (except to people who like perusing the shortcuts dialog to see what is there). See https://masteringmusescore.com/go/shortcuts/