Two OMG key committees unanimously approved the ONLY submission it received on a RFP for a systems modeling language. I guess there was a real market need for it....
The submission came from "the usual suspects": Their own member organizations like Telelogic, IBM, Artisan...all UML tool vendors and guess what...SysML is a subset AND and extention to the UML --> a profile!!!
It took the tool-folks little over 2 years to come to an agreement on how to bend the UML in such a way that it supports systems modeling better AND that it still can be supported by their own existing UML tools: drop a few diagrams and add a few.... pretty easy from a tool vendor perspective. No real changes to the metamodel of course. God forbid that these vendors need to make a real change to their tools in order to improve the practice of modeling systems. Why in fact would you? We all know that the standard UML is already good enough for anything!
Besides, with a modeling language that's really close to UML you can be sure the OMG will approve it in record time and make sure the new standard gets appropriately hyped.