There really isn't anything more to it. :)

By dropping SerenityOS as a target, Ladybird is free to make use of 3rd party libraries that don't currently work on SerenityOS. And keep in mind, SerenityOS would be unable to integrate Ladybird in this new state anyway, since SerenityOS has a strict "no 3rd party code" policy.

(Also nice: it stops being necessary to wait 30+ minutes for multiple CI runs on SerenityOS every time you post a browser engine pull request!)

In time, I'd love to see Ladybird come back as a port on SerenityOS.