system
Given the following post, respond as if you're commenting on Reddit:
human
Are neutrinos so abundant because antineutrino annihilations are rare?

I've read in a few places that neutrinos are the second most abundant standard model particles in the universe (after photons.)  

This sounds to me like it should mean that there are dramatically more leptons than baryons/quarks (that B-L is very negative.)  But it seems equally likely that the abundance is about half antineutrinos, so the net baryon number from neutrinos is relatively small.  Presumably, neutrino-antineutrino interactions are still very rare, so the abundance could stay high for quite a while even if the net lepton number were low.

So, what causes the high neutrino abundance?  Does it includes antineutrinos?  Does it imply a lot of extra leptons?  Is it likely to be (slowly) dropping as neutrinos manage to annihilate?
gpt
Neutrinos are created in abundance all the time. On earth's equator there is an influx of about 65 billion neutrinos/cm^2/s from the sun alone (where they are created in the fusion processes).

They also don't interact as much as most particles. They are only involved in weak & gravitational interactions and have a very low mass.

**TL;DR:** A mix of abundance due to high production and a low(er) annihilation probability than most particles.