The answer may be based on 4 aspects:
1.- simplicity: we all hate write tons of code for simple tasks like in java, this is the reason why we use php, importing design patterns from java/university world is good, but usually independent developers like me need dev speed more than enterprise employees.
2.- backend: how easy will be building a backend in symfony 2 vs lithium?. not always we build a facebook like project and we need our preferred framework to get the job done on little projects too.
3.- community and docs
4.- performance: scale good with the minimum