Why do streaming platforms charge for so many of the older movies that weren't even huge hits?

I decided I'd like to watch Housesitter with Steve Martin and Goldie Hawn again, but it is only available if you pay to rent. I've had that happen a few times lately with movies that I don't suspect were exceedingly popular. I could pay it. I simply don't want to. So on to something else. Funny, I could always find something to watch as a kid, despite having only 3 channels and that was on a good day - sometimes just 2! Now, I've got 4,000 channels and nothing to watch. Lol. Go figure.