Hello! So this is because most artists wanted to be recognized in their work. During the time it was a great thing to be an artist so they inculded themsleves in it.

Hey! I’m taking an art history class right now, and we actually just tackled this, it’s pretty interesting.

Very few artists actually signed their work (I believe that the only one Raphael signed was a portrait of one of his mistresses, and Michelangelo carved his name into his sculpture Pietá, but besides that, they didn’t really bother). It was actually very common for Renaissance artists to slap in a subtle self portrait in the crowd, and if you look closely, the self-portrait is the only person in the entire painting who dared to look directly at the viewer. It was their subtle way of saying “Hey, I made this” without signing the piece, because signing had yet to become a really popular thing for artists to do!

Michelangelo painted a self-portrait in his Last Judgment (he’s the flayed skin that an old man is holding…yuck), and there are a few other examples I can’t think of. Just look for the person who’s looking at the viewer, that’ll be the painter!

I hope that helps!

why not?