You do make something of a good point about nothing preventing web development becoming over complicated, except you seem to have forgotten how much that costs. Unless there is a perceived marketable difference, people will rarely push for it to be developed at all, and given the size of the average development team's backlog that pressure to develop also has to outweigh everything in the backlog as well.
The honest truth is that web development has become so complicated because that's the equilibrium point of the supply of labor to the demand for advanced features. Developing the same features from scratch using static web development methods takes exponentially longer as a function of feature complexity, and the ability to use frameworks and other more complicated tools reduces that down to being merely linear.
Web development isn't complicated because nothing is stopping it from being complicated, it's complicated because consumers want features that they assume should be simple, but are in fact very complicated.