Of course if you use a fancy webmail, Google docks or even something like Facebook it makes sense to have a full blown webapp but I personally seldom use these. But the thing is whether or not you need those feature they still bloat your web browser because you have to have it. How many websites ought to require JS to function properly out there? How many do?
Have you tried browsing the new Reddit interface on a low power smartphone? So much richness that it's barely usable. All that to display a list of titles or text comments. Or how about Discord which manages to lag in my browser despite being effectively a chat application.
Sometimes less is more. We've made it normal for people to use software that by default automatically runs a turing complete programming language for any random website you browse. If we had a tiny little bit of friction for going from website to webapp developpers and managers would think twice before cramming "rich" features and a thousand ad scripts everywhere.