To be totally and completely fair to the publishers, green lighting any game is a pretty big risk with 6+ year dev times and massive teams based in some of the most expensive cities in the world. GaaS does seem like much more of an all-or-nothing bet.
It would also be just to say that the games they do green light, whether single player or GaaS, often seem monumentally out of touch with what most gamers want, which includes going all in with uninspired, content-lite, wannabe entries in some of the most overcrowded GaaS genres. It's like they think they can just show up with a proof of concept, and gamers will pour in money to fund its continued development.