I can answer this -
because USUALLY the people riding are men with decent jobs (lawyers, media careers, similar) and they will give you a lecture about how cycling is good for the environment, yet they’ll drive their families around in large litred cars the rest of the week. oh and I’m pretty certain Lycra production isn’t good for the environment, nor the materials they use to create these bikes worth thousands of pounds but please correct me if I’m wrong.
They’ll lecture you about how cycling is excellent exercise, yet consume many pints and a burger every time they finish a ride (and many then drink cycle after the pub)
they’ll put cycling above their friends and family.
they hold up traffic (which is not good for the environment)
also (and I live in a cyclist heavy area) they weave all over the place, make it hard to overtake them, ignore cars jamming up behind them.
are impolite - I also live in a horse heavy area, and 99% of the riders make an effort to let cars squeeze by. Cyclists will just carry on as if the own the road.
theyre dangerous - as much as you might like the roads to be for everyone, cars are on the road and playing chicken with a car is just ridiculous. Cyclists forget that they just can’t be seen as easily. You might feel obvious, but it is easy to get loads in a blind spot. It’s nerve wracking as a road user!