I think at some point Heinlein must have gotten old and had to rely on sexual fantasies and his books became heavily influenced by them. I think that was first true in "Time Enough for Love", even though that was an excellent book, maybe his best. By the time he wrote "Friday" I think maybe that was about all he had left.
It wasn't a bad book but I don't think Heinlein was really the same by then. I didn't read any of his later books. That's okay though. He wrote enough really good books before he got strange.
Barry