It is indeed frustrating.

Historically, of course, copy and paste on a Unix machine was a mouse thing and followed X11 conventions. You selected text with the left mouse button — automatically be saved to the primary clipboard just by virtue of being selected, no key press needed — and the middle mouse button pasted it at the location you clicked.

This is somewhat different to having the two part motion/action of select/control-C and click/control-V. It’s boiled down to just select and middle-click. Separately, you can often use shift-Insert to paste the primary buffer.