I'm often browsing hotels ahead of actually committing to any firm travel plans, so a message like "rooms available" suggests I likely have plenty of time to keep looking (and potentially going to another website to book), but "only 3 rooms left" might prompt me to pull the trigger earlier than I otherwise would have. Of course, I am personally convinced these numbers are totally made up and just ignore them anyway.
They aren't totally made up, but they are deliberately obtuse. Hotels are ultimately the ones that control the availability of rooms sold on the platform. It is a common tactic to only list a handful of room nights until those are sold, then add more. This means that all of their rooms always have the urgency messaging. The larger chains do this at scale and across multiple third party sites. So Booking isn't really lying, those numbers are "true", in that there are "only 2 rooms left" but they don't mention the hoteliers' smarmy behavior in abusing the urgency messaging about the availability or their own complicit participation in the lie-by-omission.
Yeah there's a bit of a disconnect between what we wish it was -- a useful indicator of the actual number of rooms left, for purposes of gauging the urgency -- vs. what they use it for[0], which is to create the urgency artificially.
[0] I should say "probably" since I don't have any concrete evidence.
