USB mics could also be dynamic, the difference is the USB and internal ADC, however they are aimed at a different use case. Dynamic mics are among the best choices for live singing and miking loud instruments (drums, guitar/bass cabs, etc), while USB mics primary use is podcasting by people who don't have or need a mixing deck. I would never ever use a USB microphone for music because, sound quality aside, it could introduce a non predictable latency and possibly phase differences when used in two or more channels (8 USB mics = 8 ADCs with 8 different clocks, unlike for example a single audio interface with single multi channel ADC or more ADCs sharing a common clock), so although USB sales have increased lately, dynamic ones remain king when music is being played or recorded.