The only argument for WebForms is the need to design highly complex (read cluttered) interfaces with a whole lot of interconnected elements which in all or in part should react to changes in other elements.
A typical example would be some enterprise application (from SAP or smaller vendors). They usually have interfaces bordering madness. You'd have a hard time trying to synchronize the controls manually with JavaScript if you were on MVC. With WebForms it's by far easier.
Whether it is a good idea to build such interfaces is another matter entirely.
In WebForms element events trigger a page postback. They go to the same url and are processed in a unified manner. This is what makes the architecture very scalable.
With MVC to accomplish this you would have to set up a bunch of service urls to handle posts from different controls, then process those posts and update view models accordingly. This all involves a lot of trickery and juggling. Not that it is not doable - it is, but not on a big scale. This approach would not be scalable. Sooner or later you will arrive at the understanding you'd need to build your own framework in the direction of stateful object-oriented HTML/HTTP abstraction like WebForms.
A while ago I wrote a comparison of the two:
Migration from ASP.NET WebForms to ASP.NET MVC
Some argued it turned out to be WebForms-biased though I'd tried to keep it neutral not MVC-biased. Could be exactly what you're looking for.