I always book room for 1 person, isn't it default option anyway? I think, only for Hilton Tokyo, I added name of second guest, as Japan is a bit different.

In 99% of cases, I'm asked how many cards to the room I want or I'm given two by default.

I haven't encountered Hilton property with 1 single bed and small room but I would expect it to be in Germany and maybe Switzerland. Single rooms in hotels are quite popular there and it saved me quite a lot of money and got extra availability when travelling alone. I was able to book rooms in sold out hotels, because only singles were left.