Probably because you were a new customer within that 30 days window where they tell people no to re-apply in case they had gotten a rejection. Most probably because your account was still new, just a guess.
Not sure if we can get anyone who had an older account and got hard searched.
I don’t really know what happens but I get no hard searches. One of the reasons that have made me stick around.
I tried additional accounts with Natwest and RBS, got hard searched each time, and so did Santander and FD.
When I got a second Nationwide account in 2023 and then a credit card, they just did soft searches for identity check and affordability. Previously they had hard searched me for an additional current account and the first credit card I had with them that I later closed.