why are all the shortcut keyboard commands grayed out?

If you are asking about the keyboard shortcuts listed under the headings found in the Menu bar – File, Edit, View, etc – many are grayed out because they are contextual and dependent on you having selected certain items or for certain conditions to be met before they become active.

For example, in the Safari browser menu bar, if I click the Edit menu right now, I see that the Cut (⌘X) and Copy (⌘C) commands are grayed because I haven't selected any text or other object for that command to have an effect on.

You will see this as normal behavior in the Finder and all of the apps on your Mac and in other computer OSs.

If you are asking about some other keyboard shortcut commands, please elaborate and clarify your question and someone will be happy to assist.

Applications, files and folders that are integral and installed with the macOS cannot be deleted. So if you have selected one of these, then that 'Move to Trash' command will remain grayed out and inaccessible. This is to help keep us from accidentally - or on purpose - compromising the integrity of our computers.

Most other apps, files and folders should normally allow that keystroke to function unless there is a problem.

If that is your case, the first thing to try will be to simply reboot your Mac.

If a simple reboot of your Mac doesn’t fix things, see if the problem still happens in safe mode.

How to use safe mode on your Mac - Apple Support 

Safe mode will often correct weird software behavior by forcing the OS to do disk repair, clear caches and other housekeeping and disables acceleration and third-party mods. When you're in safe boot, the machine won’t be at its best performance, especially with graphics, but that's expected.

Does the same thing happen while in Safe mode?

You can exit safe mode by restarting your Mac normally.

Have you tried selecting the item you want to move to the Trash bin and using the key combination of ⌘+Delete? I find it quicker and easier than shortcuts.

Also the key combination of Option+Command+Delete will empty the Trash bin.