There have been quite a few variants, but the vast majority don't get labeled as variants of concern. That's why it appears they're skipping letters. Because those other variants aren't considered especially concerning due to being isolated or something else, so you probably don't hear about them unless you're doing research into the topic specifically.

This is from back in July, and they have made their way further down the alphabet since then.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8342008/