I can't help but think, and I could be 100% wrong, that EA charges Microsoft, and wanted to charge Sony, a fee to carry the service and Sony didn't want to pay it. It's a business decision that Sony thought wouldn't be best for them. Granted it's taking away the decision the consumer could've made if they wanted the EA service for not.
Why would EA being charging Microsoft? What possible service could they be charging for? MS are letting EA sell games through their infrastructure. It would be like a shop charging the mall owner rent. I don't think even EA has the balls to try that.
The only way EA could charge would be if they are giving MS a cut of their sales, which still doesn't really make much sense. I think they reason Sony said no was because it is a competing service (if a crappy one) and they don't want it drawing customers away from PSN.
There is a second possibility outside downright "charging them", which is EA does not want to pay for maintenance fees of PSN (currently, publishers pay Sony for the bandwidth users use to download demos, trailers or games). Since EA Access would only use PSN for login, they may want to renegotiate so it doesn't pay those fees, and Sony didn't wanted to.
The reason MS is different is because they never charged the publishers for maintenance of their online network. That is the reason PSN remained free for the public while XBox Live was always behind a pay wall.