I agree, there has been a clear, negative direction of stacking complexity in Web development for the past 20 years. It's one of the primary reasons Wordpress has 1/3 of the Web and there is a cottage industry of developers that specialize in just hacking at Wordpress to make it do things it's not particularly great at. Most people and most businesses can't come remotely close to building their own high-functioning sites (from scratch) in a cost effective manner, while getting all the critical details (eg building for SEO) right. So you get an obese do-everything CMS, and throw in some plug-ins, to sort of shim the problem.
Why is Shopify worth $150 billion? Well, other than the bubble, this effect is why. People can't easily build their own ecommerce sites, can't integrate everything they need to, in a way that doesn't cost them a small fortune.
Wix is a pretty mediocre service, clunky and slow. It's worth $15 billion? How in the world does that happen. Well, building sites is super difficult for most people. The opportunity to make that problem better is, apparently, huge.