Usually, it's to confirm the residency, in case that the player use an IP masking tools. Let's say that's another layer to be sure that the player indeed breached location ToS, as well as to put face to names, in case the abuser created another account.
As for accessing from a restricted jurisdiction, I actually did not see their terms where they didn't allow UK players.
I asked on live support before deposit if I was allowed to play sportsbook from the UK and they said yes, but on the casino side many providers would be unavailable.
OP, do you happen to have a screenshot of this conversation?