Blockstream is way more than this. they include 40% of core devs in addition to 3 of the top committers. they are in a position to influence all future decisions regarding upgrades to Bitcoin, and that includes blocking competition that could make SC's obsolete.
their incentive being to sell as many SC's to any willing buyer. that is what a for-profit does.
Sidechain is better tech than what competition as to offer at the moment.
To be quite honest, I can hardly see how something could compete with the sidechain model the way it could be implemented right now.
Sidechains are a very natural extension to the Bitcoin blockchain. They are the most fitting application layer on top of Bitcoin's TCP/IP.