Thanks to 
@TheBreadmonkeyBennu I learned of the existence of 
@altbot !
Some people have to do a lot of work to get text typed out, and find posting images much quicker - it makes total sense not to suggest someone typing with a sip-puff or other switch to have to also fill in the ALT text.
Also sometimes we're in a hurry. Or we're wanting to report on a fast changing situation. Or whatever other myriad reasons! Looks like altbot can help :)