Good point. Most of the publishers signing additional exclusive deals with Epic had very succesful games on EGS in the past: Deep Silver had Satisfactory and Metro Exodus, Gearbox had BL3 and Saber had WWZ and Snowrunner. All of these publishers were very vocal about these games doing better than expected on EGS.Maybe the prices for securing exclusives went way up. We're almost two years after launch, many devs will know how well EGS exclusives have sold so far.
But what about other devs and publishers? Annapurna's recent games are all multistore. The Solitaire Conspiracy from the John Wick developer is on Steam as well, despite looking very promising. Most other recent EGS exclusives are first deals for the devs.
It is possible that Epic wants to become cozy with as many popular devs as possible. Or... most games didn't do very well on EGS. The coupons may indicate the latter, but we honestly don't know. Lot's of people seem to be using Epic's coupons, but based on what I read on forums they seem to be using them for AAA-games most of the time (Ubisofts games, RDR2 etc)