There is a huge general misunderstanding in the profitability of directing hotel bookings vs flight bookings or other types of travel consumables. Rate parity and high commission rates mean that directing hotel rooms is hugely profitable and Expedia (hotels.com, trivago, expedia) and Priceline (booking.com) operate as a duopoly in most markets. They are both marketing machines that turn brand + paid traffic into highly profitable room nights.
booking.com is such a piece of shit in so many ways: strip-mall aesthetics, horrible data quality (firsthand knowledge here), huge commissions for hotels, and yet, it's a fantastic business.
Probably a good lesson or two here.
Either way, if prices are roughly the same on most sites, I'll go for something that just lets me get the job done. I couldn't care less about aesthetics and commissions if other places can't give me a much better discount while also not getting me angry using their site.
I'm sure it fluctuated since, and from friends still working there, i would guess upwards.