Depending on how far in advance they had to start laying seeds for phases four, five, and whatever, it's possible they had to dig up a threat bigger than Thanos with a more limited toy box. And they introduced the original Guardians already, and Thor ended up with the Guardians at the end of Endgame, and that team-up faced Korvac in just his second appearance. Like I said, I'm not vouching for accuracy, just thought it was a fun thing to discuss.
