And +1 for failing fast. It is failing slow that’s the disaster.
When you have people using your stuff, you have to decide whether you care about them or not. It’s ok not to care, you don’t owe anybody anything, but if you lead them on or give them the impression that you do, then they are invested in something because of it and it would be pretty shitty to just disappear. You still can, if you like, but you should at least do it consciously.
If you have people the impression that you would support something then you need to be clear with them that this isn’t actually the case, otherwise you’re a bit of a dick for leading them on. It’s perfectly ok to just throw something out to the world without supporting it in any way and it’s also ok to step back from something you did once support, but you should at least communicate this so people don’t get the wrong impression.
"What are you doing?"
"I'm painting, some people bought my pictures"
"So what's your exit strategy?"
Perhaps what happened here is a side project grew into something larger, it's now just a project, and he fell into putting more time and effort into it without making a conscious decision due to popularity - perhaps that's when it can bite you, when you realise you don't enjoy it anymore and it's become one sided.
I think side projects should stay as small as possible unless there looks to be a real potential for both yourself personally and the rest of the world - even then failing fast feels like the best idea.