They have very poor acommodation compared to a cat.
They are bloody awful things to "park".
They are less seakindly than cats and prone to pitchpoling in heavy weather.
As a racing machine......awesome
As a practical cruising boat......hopeless
Since the death of the ORMA 69 class trimarans are getting fewer. The French still sail a lot of them, but in England the interest and financial support was just never there for it to take off. I reckon the last big multihull to be built in England was Team Philips.
Trimarans are great boats to sail, fast and responsive. The down side is they have very little accomodations for their size and they carry weight very poorly even worse than a catamaran. Also, as stated, unless they are of the folding kind they are very difficult to park in marinas.
For cruising they seem to combine the beam and handling disadvantages of a cat with the heeling disadvantages of a mono - in other words the worst of all worlds.