Because the UNIverse Premium model is the one I know I like. How can I assume that I like a cartridge I have never heard more than one which I have heard several times and I know I like?
To me, new is not necessarily an improvement. To me, different is not necessarily better.
A carbon fibre or diamond cantilever probably means “more resolution” and “more neutral” and “greater extension at the frequency extremes.” Those differences, to me, are not necessarily consonant with naturalness and easier suspension of disbelief.
The fact is that I have consistently preferred components which do not go too far in those sonic directions. (Although the system I am planning to hatch goes a lot further in those directions than my prior system which I had for 18 years.)