I don't think it is ruining the experience because it's easy to not allow them, my question is: how is it that so many people are clicking allow that businesses see it worth the annoyance to add this to their site. That's what baffles me.
Maybe the problem is that you don't know how few will allow it, before you add it to the site. When you know that nobody cares, all the work is already done and removing the feature would actually require some more effort.
Probably because they don't read it and think it is the cookie notification.