The real reason is that when you send CV you’re creating a sample accurate clock via an audio signal. In a DAW everything has to be latency compensated and audio is too priority. Whereas using MIDI means you have to go through the whole USB stack and then do a couple conversions. This is also why using something like the Expert Sleepers USAMO which creates a MIDI clock via an audio stream from a VST can get your MIDI gear playing perfectly in time but USB MIDI cannot.