Maybe because you'd have to go the extra mile to outdo competition and gain a majority market share.
It isn't just the 9-5, but the idea that your job stops when you leave the office. If people see it as a transactional relationship only, it means there's less investment in the product
Why? Surely it's doable within the 9-5 schedule (plus some people for the on-call rotations), it would just take a bit longer?