@A1RW0LF9, from a strictly financial point of view what EA is making makes sense. Strategy wise, it is not the best one to please the clients.
Financially, we have to understand that when we buy from Steam we are paying to Valve, which takes a portion of the sale and pays a negotiated share of it to EA. If EA wants to "validate" a currently Origin validated EA Play subscription on Steam, Valve would ask for something which EA is definitely not willing to pay.
If you want to have an EA Play Subscription through Steam you will need of course to pay for it in that platform (which is not owned by EA). The comment you made about XBOX and PC is not comparable, as both platforms are managed by Microsoft.
What might happen in the future is that with time, when it's time for renewal, you switch your EA Play from Origin to Steam. Which makes sense for me because, as you say, a normal person would prefer to have a single platform from where it launches its games.
What could deter people from doing this is if not the subscription, but the ability to launch the games and manage the games could be done in either platform, regardless of the subscription where the game was bought. This means that for financial transactions like buying games, buying addons, etc) you would need to manage the game where you bought your subscription, but, and this is a great but, you would have it available on both libraries where the game could be recognized (this means that EA Games which are not supported on Steam would not appear there). If your EA Play subscription expires and you have games bought through it on your Steam library, they would disappear and the same applies to games bought through EA Play on Steam which would disappear from Origin. So this way the problems in the financial approach of the cross platform would be isolated and the flexibility that each player could get to manage both platforms would be an added value.
In my case, I'll be honest. In the scenario I am seeing, once my subscription expires next May, I will end it and buy it on Steam. If EA enables crossplatform interoperability in a way similar to the one I suggested, I will keep it here and manage things on both platforms.