USB-C transfer speed can far exceed lightening USB2.0 speed (60MB/s duplex), offer better power delivery (with circuitry support) and of course, one less cable to deal with. With Apple pushing ProRes, meaning 120GB/30min, lightning and even wireless transfer would be way too slow.
Lightning can run at USB-3 if they'd let it. See the iPad models from 2015 to 2018. While we're at it, what's the transfer speed like on the iPhone 13 Pro and Pro Max?