Ranting online about stuff often brings out a lot of "this happened to me too" stories that sometimes shed light on things or, at the very least, provide for a moment of commiseration. That's the main reason I do it. I mean, I'm not going to change the mind of a national chain of home improvement stores by ranting on Mastodon. I'm not going to change their mind by calling customer service, either. Or leaving a review on Yelp or something. There's little anyone can do except commiserate, tbh.