It’s not a conspiracy. It’s a well-intentioned but poorly thought-out design for basic 1990s word processing layouts that accidentally blew up to describe entire application GUIs, and now it’s not in the interest of the stakeholders to try to do anything about it.
It’s the same kind of growth pattern as government bureaucracies. Those are largely not conspiracies either, despite the occasional optics.
What you’re describing is the organic growth of a platform. The web is undeniably more complex than it was twenty years ago but needs are more complex too. Yes, the complexity does benefit major players but that isn’t the reason the complexity exists.
It’s ironic you’re saying that CSS is some form of vendor lock in. I have to imagine that if Google proposed a new layout engine for the web tomorrow they’d be roasted to kingdom come for their attempt at taking over the web.
It’s the same kind of growth pattern as government bureaucracies. Those are largely not conspiracies either, despite the occasional optics.