I have heard it in abstract art, which is sometimes said not to be real art; and fields that sometimes aim for photorealism such as landscapes and portraits, where people will say "You shouldn't waste your time with that, just take a photo."

It's all bullshit. All art is valid, whether or not it is popular; there are many reasons to make art, and not all of them involve money or even other people.

Also, bear in mind that the art world is often vicious. People who grow up with art teachers shredding work and students alike in critique are likely to think that is a normal way to treat art and artists, if it doesn't drive them out of the field altogether. It is not healthy but it is very common. I've written about that in a few pieces.

It's worth combating negative art talk anywhere you hear it. There are better ways to talk about TTRPGs and their art. I mean, look at Kickstarter, it's all about "We are making this awesome thing with beautiful art, would you like to come and play with us?" Hell yes. I just backed a video game, and I don't even play video games, because it's subversive but also the art nails the stylized-saturated style of southwest art that I've picked up on postcards while traveling.

For an example of more positive art talk, I just did a piece about some paintings I bought at a rummage sale. :D