The whole thing is entirely dependent on the dates of your stay. Discounts of more than 25% are very rare for long stays in my experience.
I know in the current situation it’s a poor example, but if your stay dates include a big conference, event or something similar, the hotel won’t be very keen on you staying there since the would charge sometimes up to 4 times the normal rate, so if it’s a 4 day conference smack in the middle of your stay dates, the hotel won’t be keen on you as a long stay guest.

Another reason why discounts at places like FS, MO or similar brands is simply protection of brand identity / rate integrity.