I live alone and managed to find uses for 3, and I sleep on a couch in the living room, so am not using a bedroom for a bed. If I slept on a bed, I'd be able to make use of 4 bedrooms.
One is an exercise room. It's the first photo here [1].
The one in the second photo is the electronics and music room. Table on the left for my electronics stuff, and piano on the right (and guitars out of frame on the right, along with a bookshelf full of music books).
Third bedroom is the library, covered by the next two photos. 10 bookshelves.
I could easily see two developers use 6 bedrooms. 1 for sleeping, 1 for a library, 1 for exercise, 1 for a join hobby for interest, and 1 for each for a hobby or interest that the other doesn't share...and that's without even considering using a bedroom as a dedicated office for working from home.
[1] https://imgur.com/a/lVmMv86