why do people put the extra X in there? indolence?

My best guess is it's become a sort of linguistic meme, poking fun at incels who'd ramble on about things like "looks-maxxing".

Or maybe it's a combo of that and "min-maxing" from gaming communities. The extra X makes it more maximum. LOL

Taxing, faxing, relaxing...

"...Shootin' b-ball...

When a couple a' guys, who were up to no good...

Started making trouble in the neighborhood..."

--Prince William Smith of Bel Air