Anyone who can see the uuidv7 can determine at what time it was generated. You might not want that for things exposed to users.
You can hand out uuidv4 to clients without revealing anything.
Entropy. You loose bits to a known source, which reduce entropy of the UUID.
128 bits is a lot of entropy to go around, though.
I do feel 74 bits per second is enough though. That would require 2^(74/2) = 137 billion UUIDs generated in a single second for a 50% chance of a single collision.