Is that true, or the reverse? That web apps became a feasible thing only after consumer hardware, esp phones, became performant enough to handle loads like that (which lead to less and less offloading to servers)?
So in my view, browsers became capable, but then plenty of "heavy" web apps appeared, which required more beef in the machine.
That's also the typical way it goes: current hardware being okayish but not great is one of the strongest drivers for better hardware. Whether it is gaming (PCs), camera (smartphones), the web bloating (both).