1. Leica glass creates a different image that many prefer (I'm basing this on stills and Primos -- the new lenses are sure to have similar characteristics) = happy DP
2. Size -- the Leica lenses are considerable smaller/lighter = happy camera op.
3. Scales -- the Leica lenses essentially share the same focus scales across their lens line -- crazy but true. An AC can get used to the focus distance on the lens(es) and achieve an extra degree of muscle memory with their focus pulls = happy AC
4. Cheaper than Master Primes -- people think these lenses are expensive; relative to their closest competitiong (Master Primes and S5i lenses) they are not expensive--they're actually pretty reasonably priced = happy PM
Add points 1-4 = Happy Producer
Oh -- and you can easily stick nets on 'em too.