You are probably just not noticing them
Actually, it is possible not to have them. This is the first year I have seen them here since I got horses here. That's about 5 or 6 years now. Where I was previously, we had them every year, some worse than others.
I still don't buy the motor oil solution. Ok, it might work -- probably does actually, but I am not putting poison on my horse when there are other options. I don't want the horse to eat it, nor do I want it in my fields.