Follow up: I've never heard him be called William the Bastard before 😂 what's the story behind that?

I'm not sure what you're asking. Are you asking why he didn't just give up and surrender to one invader so that he could fight the other under them?

Why not such a decision?

Harold II most likely believed that he could successfully repel the invasions, and he almost did so.

After all, he successfully defeated the Norwegians at Stamford Bridge, and though he lost at Hastings, all records show that the battle was a close won thing that lasted the better half of a day.

In fact, according to most historical sources, the Battle of Hastings was only lost when Harold’s brothers fell for William’s reigned retreat, of which he had only done as a last ditch effort before retreating himself. This caused the Saxon flanks to break formation and thus allowed the Normans to use their superior calvary to disorganise and break the Saxon host.