Why SCA is better than other services composite applications? We can connect components in BPEL execution environment or just using some tooling that enable an easy connection of various components to some ESB?
The idea is that SCA is complementary to other technologies rather than being a replacement for them. Take your BPEL example. If I want to orchestrate distributed services over WSDL defined interfaces then BPEL is a good solution. If you want to drive services over other communications protocols with BPEL then it becomes a bit more tricky. Create an SCA component with the BPEL process though and you have the service and reference flexibility to use a variety of bindings with that BPEL process. You can then use you BPEL process to orchestrate components over RMI, CORBA, JSONRPC etc.
You could do similar mediation with your favourite ESB also. SCA doesn't preclude this. What SCA does add though is a model of the wider connected application using an OASIS specified (not quite a stand yet but getting there) assembly model.