The most common use case for a RPi is people who just want to hook it into some electronics and play a bit with it, very much like a modern day Arduino. The second most common is some kind of server be it simple SMB share, DLNA wtv. The 3rd case is custom images like retropi, home assistant etc… In the first tow having SSH by default greatly simplifies things.
People who deploy professionally / on scale / create customs images for other things are tech savvy enough and know how to disable SSH - no need to have it disabled by default.