Interestingly they have 25 to 9-pin adapters and the majority of DB25 devices I worked with were fine either way. So, the devices generally used 9 pins or less (or at least 9 or less pins were "important").

There are, of course, devices that use more than that, but most things seemed to use less. Maybe that's part of the reason the 9-pin became more standard.

Frequently only 3 pins are used in a DE-9.