But that doesn't go into clipboard history. And severely restricts what you can do between copying and pasting in general (very importantly makes it a pain to do replace (i.e. select+(implicit-delete+)paste)) as any intermediate selection before pasting destroys your Primary Selection. And if you realize you did that, recopying takes manually reselecting the text, or the otherwise-never-used ctrl+insert to recopy, instead of just repeating the same old ctrl+c as you always do with the clipboard in any sane application.

Of course still a nice option (esp. in terminals where the proper copy/paste are nerfed and selecting for editing is annoyingly not a thing), but far from a replacement for the proper clipboard.