Why can't I just quickly LIKE a photo - posted by a model/photographer/mua - by one click like in almost every other creative photography app in the world? For almost 20 years I just don't understand. 🤔

Have you posted this inquiry in the Site Related forum?
https://www.modelmayhem.com/forums/thread/4

It's pretty unlikely that anybody meandering about randomly on the other forums (like me) will have useful information for you.

I don't know how or why anything is done here. For me, it's a place to park some images, network with a few potential models and maybe post like this one once in a while.

you like photos in your Newsfeed. That is under the "my stuff"

To show support of the photo, I go in and make a comment.  That way the photographer sees the recognition.  But this isn't social media like FB or Twitter.

You should make a list and then add the photos you like to it  Maybe call the list "Photos I Like". MM will then send out a notice to the photographer/model so they will know. In addition, your list will be added below the photo you like.