Why complain now?

There’s a concert promoter in London that’s been spamming me for years and years. Most of the time my spam filters take care of it and I never see their mail. Every once in a while, though, one of emails gets through and ends up in my inbox. Usually I move it to junk, curse at my filters for not getting it right and just go on with whatever I’m doing.
I suspect this is more common than not with most people. Those lucky enough to have a “this is spam” button can make the mail stop by clicking it. Others, like me, just have to delete it and move on.
Sometimes, though, I get to the point where I’ve had enough. I’ll send in a complaint to the sender or their provider.
I have to wonder, though, how many people react to email negatively and hit “this is spam” when they’ve been ignoring mail for a while. This can complicate the lives of senders (what doesn’t?) because the “this is spam” isn’t in reaction to a specific email, but happens due to circumstances outside of the sender’s control.
Delivery is an ever changing field, and it’s just getting more complex and harder as receiver tools get more sophisticated.