Some traders prefer trading in their region for smaller trades so they don't have to switch servers or add people as friends just to trade.

Idea is to add region section All/Americas/Europe/Asia - something like OG Hardcore has now.

Servers are connected so default would be All with the option to select trades according to region.
This could also serve as an indicator on which region would the trade game be, easy to know if you need to PM btag for fast trade from other regions.

Small quality of life upgrade to the website, not paramount for sure but would be nice to have.

Sorry, not necessary as you can just add their btag or simply exit your game and restart it on the region.
People would miss many items having it all split up since they are all connected as you say.

Has been suggested before several times.