You'll get people signing on for short cameos. It's meaningless and gives their profile a short boost. If the property fails, their personal reputation won't take a hit.
When you're asking them to invest some serious time and effort in a main character, it's different... They start thinking about the actual quality of the script. If they think it's crap, then they know their inclusion will be more associated with it.
Respectful credit to Adam Baldwin for being above that apathy, when it came to 'Requiem'.
As for political correctness, I agree with Hubbs that the casting demographic looks dubious, at best. It's like they're reversing the roles for the sake of it, not because it adds anything to the story, except failing to understand why those roles succeeded in the first place - what we know and have seen of Hemsworth is strongly pointing to this. We could be wrong in those assumptions, of course, but it's as was said above: He seems to be coming across as a 'hunky nerd' stereotype.
That's what people seem to be objecting to here. The fact this all seems so horridly predictable and formulaic, when the original film is so iconic because it broke the proverbial mould for comedy.
I certainly wouldn't object to an all-female team, but the way they're going about it just seems destined to fail - and when you feel that way about something, you wish to high heaven that they weren't doing it with a franchise which is so beloved. Everything I've heard about this, so far, makes me think they could have easily just made it something completely original.
And, sadly, those leaked Sony E-mails which referred to the plans for this series, only confirm this. They aren't doing this because the scripts are necessarily any good. They're doing it because they want not just one sequel, but a spin-off, just to make money. That's arse-about-face. They should get a script which is good enough to conceivably make a profit and then finance it.
And let's look at the female characters... There are a number of actresses I could think of who have excellent comedy timing, but none of these ones strike me that way. So, again, yet another factor which feels uninspiring about this particular production.
And, yes, I feel this way about the spin-off, too, which is already in production and has male leads.