That's really not true at all. For many artists social media is the only or best way to gather a following and advertise their products.
It takes a ton of hard work to build that following since the art market is heavily saturated, especially post-covid, but social media is the best tool for the job.
OP just doesn't know what they're doing and thinks it's a walled garden.
Yes, it's called running a business. Spending money on advertising is a requirement if you want to start one.
It doesn't take much money if your work is good, though. My wife is a tattoo artist and she built up her following in just 1 year to the point where she's booked out 2 months, and she only promoted posts for $20 or so here and there.
Self promotion isn't an easy thing to do, so I'd suggest reading some how-to articles about how to grow your Instagram following. It requires a lot of work, to the point where managing your social media is a very large part of the job.
At the beginning my wife spent about 75% of her time on social media, while the other apprentice didn't. Now the other apprentice struggles to have more than a few appointments a week.