Are you not advertising that it's 60% in-office? It seems surprising that multiple people would see that and go the whole way to an offer without self-selecting out.

We are.

I think in both cases people were selecting between us and another job. One said he was taking another job for 10k LESS (GBP) but full remote.

(As always, the stated reasons might not be accurate)

The cost of maintaining transportation and the unpaid hours from a commute are quite significant. Depending upon their circumstances they could be taking home more money even being paid less.

100% this.

Here in the UK, just not having to live near London will save you enormous amounts on rent/mortgage as well.

I'm in the office full time (I actually need to be) and I pay 700 a month just in rent on a crappy room not too close to central. That alone is the equivalent of about £17k before tax, and I am a single guy who doesn't mind housemates. No thanks.

It seems likely that candidates are comparing offers, which requires them to get a decent amount of the way through the hiring process.