Or is it that the victims pest warning system is currently winning the biological arms race, in which case how are mosquitoes able to successfully reproduce? Or is it that mosquitoes have evolved such that their spawning numbers offset the difficulty they have biting?
Biology is hard.
They have! For the most part you don’t even notice mosquitoes biting you until after they’re long gone, the part that itches is from the mosquitoes saliva that is left behind! They have evolved to the point that you should never even feel them sticking their proboscis into you so if you actually catch one biting you it’s probably because something went wrong or you just happened to see it land