Every game/platform has to have its account and link it (via table) to other accounts. So you might have an EA account, and under that have registered XB, PS and Steam accounts so you can support cross-progression etc. Every service has its own protocols too, so connecting between PS and XB for chat and whatnot adds complication. It's no longer difficult per se, but it still is a requirement to have an overarching account to handle other accounts.
The only solution is a Gaming Passport; an open protocol agreed by everyone. I expect there's too much legacy baggage, plus no incentive (locking people to your account helps lock them to your ecosystem), plus different requirements, for that to ever happen.