More turns means that it is harder to manufacture and more prone to breakage. MOST of the top cartridges are low output. I would have agreed with Metralla until I got a step up from Bob's Devices. My phono stage has plenty of gain but the step up makes a LARGE improvement. See also recent discussions in Stereophile about transformers. Many of the top phono stages have them built in.
Why a low output M.C. rather than a high output?
Since many cartridge manufacturers make both High and Low output models why would someone prefer the low output which very well could require a step up transformer along with another set of cables? Wouldn't resolution be less this way with the extra step?