You can try and model things on the idea of rational experienced senior devs all making tech decisions based purely on hard evidence-based demonstrations of material benefit of new tech over old tech, but reality is much softer than that.
Another factor is that Google's hold over SEO allows them to drive change through SEO requirements. E.g. there's always been a lot of overlap between new tech introduced and Chrome and requirements for Google search indexing, and that stands to increase with things like Core Web Vitals,
> rapid change in the standards is not really a sign of monopoly
Your statement here seems to be just picked from the ether and not actually based on anything in reality: there's no reason rapid change cannot be associated with monopoly.
There are many differences between how Google is approaching tech and how Microsoft did in the late 90s / early 00s but the its worth noting that second E in their infamous Embrace, Extend, Extinguish strategy most certainly involves rapid change in standards. This is hardly the only example, but it's notable I didn't even have to pick a different industry to find one.
However web dev practice has been driven by Facebook and its quasi-functional programming advocates for at least 5 years now (Redux/React). There's a whole generation of Web Devs that don't know that DOM Event handlers can be objects that bear the handleEvent interface because React prohibits that application for example, but that's a whole world of memory efficient async handling rather than generating throwaway functions for ever little thing
Rather novel weapon. This won't work, rapid change will just leave the large base of web developers behind. Tutorials and practices based on the Old Way hang around for decades.
Google putting out a standard is only going to help them if it is (a) in demand by web devs and (b) competitive with the old way of doing things.
I don't particularly like web apps, but they are a new field and rapid change in the standards is not really a sign of monopoly.