Earlier quoted context omitted.
There is no trend towards lighter frameworks. Frameworks were originally being developed by people with high-end needs. They are then also adopted by people with low-end needs, who conclude that the framework is too big and complicated for them, and start developing/adopting more light weight frameworks. This market is still young, so there are no dominant players like Rails, Django or Symfony yet. It's more a matter…
As a Django user, I hear a lot of people rant about microframeworks, and I have to ask, why? I was amazed at the productivity gains and organization Django brought to my code. If all that bloat is getting in the way, why not go back to CGI? That must be the most minimal of frameworks.
Another problem with many of the existing big frameworks is that they don't do single page apps too well - A lot of stuff I do these days just doesn't need to be designed around the notion of composing templated widgets server side. I just want to ship static html/tpl/etc files and dynamically built data. Wrapping my head around pretending everything is a full page build gets a bit frustrating - why is the response to a query a view or *view? It's just a serialized model I'm pushing over the wire, or a remote function call. Pretending it is a view is a layer of cognitive overheard in between the work I'm doing and the data I'm using.