First I will speculate - both casinos wanted oversize chips for these. MGM already had a baccarat house mold so went ahead and used it.
Wynn's oversize mold did not say baccarat in the mold itself. They probably didnt fancy paying $30k for a mold just for these chips so they used the existing one. Probably had to get a waiver from gaming to allow the oversize not to say baccarat.

Anyway, I dont believe ANY of the $8 chips from anywhere are/were ever used on a baccarat table. $7.60 payouts are way too much hassle
Those casinos that do use them do so on Pai-Gow tables (where betting in multiples of $8 is good).