WIDESCREEN splitscreen

Can someone explain to me why black bars are present in online halo 2 anniversary, halo 3 campaign, halo 4 campaign but not present in halo 1 online and campaign despite it being the oldest of the bunch? Is it just die to game companies killing off couch multiplayer or what.

halo 1 was not intended for widescreen use but 4:3 .
so the fov is really big in splitscreen
in the newer halos they try to fix this with a simulated 4:3 screen.
the original halo 2 used left/right splitscreen ( which was horrible).

But it looks better in halo 1, wtf.