1. Marketshare does not define leadership in product design, functionality & quality.
>>Why is everything so carved in stone?
Each daily build, and major version of Houdini is modified in someway, sometimes subtle, other times more apparent. The reflected question is why should everything be so fluid and change? See point 1

Edit:
>>All I see is, Nuke is market leader
Nuke is mainly the leader as Apple killed off Shake in 2006, Hardly anyone was using Nuke and pretty much everyone was using Shake. If Autodesk kills off Maya/Softimage then Houdini is now the leader of the rest of the 3d software.