As you said, providing liquidity is a useful activity, and empirically Monero has had relatively high volume and relatively good liquidity (by which I mean strong order books) for most of its lifetime. Contrast that with coins that may have high volume during pumps, but turn into are ghost towns with pathetic order books the rest of the time.

This thread also happens to be the most popular alt discussion thread on the entire forum by a wide margin. Is that a coincidence, or is having a good, active venue where traders and long- and short-term speculators can communicate (sometimes seriously, sometimes more socially, sometimes ignorantly, sometimes informatively, sometimes manipulatively) part of what contributes to that liquidity?

I'm not sure it is really possible to separate out the factors that have made Monero as successful as it is.

It's certainly not for everyone though. If I were forced to consistently read the BTC wall observer thread, suicide would become an attractive alternative.