Why hardly any anaphylaxis in hay fever?

Hi all, I am not an immunologist but I have a question that is bothering me for some time now, and I cannot find the answer online. I hope you guys can help me out.

Anaphylaxis can happen as a result of exposure to certain foods, insect venom and medicine but hardly to pollen. I was wondering why this is?

Is it due to a different mechanism of antigen uptake and presentation or is there just a really low concentration of pollen in the air? Or are pollen not getting in to the bloodstream and thus not causing anaphylaxis?

I hope some of you might know an answer :D