Could the shorter length actually help with it being easier to produce, if they actually produce?
They can keep the HMs on their toes by switching up things more often and maybe stop some of the predictable alliances and usual celebrity bullshit from getting in and killing the spontaneity. It could be more interesting for the HMs as well... putting people in a house without social media and cell phones is probably hard for the younger ones especially who are used to flicking through their phones all day and so aren't accustomed to needing to entertain themselves or others without it
Edit: That doesn't mean they can't lengthen it later once they find a workable formula