I really fail to see your problem here. "There is no activity in that community" maybe that is because everyone posts to c/programming instead, causing a negative feedback loop. Crossposting doesn't cost you any engagement.

It's also peak entitlement to berate the guy doing the most amount of work on this instance to keep it active and going for not posting enough content just because you didn't like what the bot told you. A single bot informing people that there are other, more suitable, communities that would benefit from a crosspost isn't spam.