I fly a often, usually twice a week, I often fly first class, I often fly coach. Security has never treated me differently when I fly first class.
I’m not saying it doesn’t happen somewhere, maybe it does. I just haven’t seen it.
Might you be seeing the pre-check line for those who travel often? That is the only expedited security I’ve seen.
I once flew with my my sister and brother-in-law and we used a special check in line. But I think it had to do with being a member of some club of the airline or an American Express club........