If I had a 4 or 5 br I'm sure I'd find a use for them as well. To each his own and glad you are enjoying those spaces instead of the crackerboxes out there.
As for "far more" I guess I should stand corrected. It sure seemed that way when we were searching but to be more accurate I just did a quick search and found "far more" might be an overstatement.
Over the last 90 days on Gohome I found (across all over HK, not just HK Island or the areas mentioned)
2br <$50k 90days
7,014 / 227
3br <$50k 90 days
6,345 / 1,746
4br, <$50k 90 days
512 / 336
While technically there are slightly more 2brs than 3brs (the first number is total units available) when you add the OP's criteria of size of at least 1200 sq feet you'll see there are actually far more 3brs than 2brs, although a >1,200 2br seems pretty rare so the numbers are a tad skewed.
The point I was trying to get at was more as to whether there was a specific need or desire for a 3br (den, guests, storage) or whether they were just sort of going by what they had before they moved over. We moved from a spacious 5br place to HK and got a 3br on the assumption we'd have guests or that the kids needed the extra room. But it has turned out it would have been far cheaper to just put the guests in a hotel than to pay the extra in rent and the kids ended up sharing a bunk bed and are more than happy living that way. We've actually been quite surprised how downsizing from our larger place to a smaller one has gone, so much so that we're seriously considering a 2br for our next place.
Of course your mileage may vary, but it might be worth considering.
Good luck with your search.