Not really, it was experimental and only released recently (end of last year?). You can't really build experimental features with potentially breaking changes or even a complete removal into a CI pipeline without a lot of risk.

The main issue with Cypress handling this is, from what I understand, one browser per domain which can cause huge memory usage (which Cypress already has an issue with). Once you try parallelising multi-domain tests you run out of memory on developer laptops pretty quickly :(

But yes ultimately you are right, multi-domain is available, it's just those edge cases that get you once you go beyond simpler cases.