It obsoletes older browsers. For a while it used to be you could browse the web with almost anything, even a 10-year old Netscape. Now it's the norm that a 4 year old browser isn't supported, because of new APIs and JS syntax.
Websites evolve, and that's the choice of developers around the world. You have no right to complain if you don't keep your software up to date to a reasonable level.
If you want to use 4 years old software, you MUST accept things are broken and that it's your fault. Try downloading Firefox 1-10 and see if they work today ;)
But if everything operated like the web ecosystem, we might consume 100% of our time and money just on upgrades.
And it pretty much guarantees there will only be a handful of vendors, because it's very expensive to stay current.
All other things being equal, a decade is preferable because time/attention is valuable. Frequent and in particularly non-careful updates can put individuals and in the grip of a form of the red queen problem rather than being able to spend time/attention on new levels of capability.
I don't particularly mind some obsolescing of browsers where JS is concerned, and browsers in general have done a remarkable job of retaining backward compatibility.
More problematic, though, is the attitude that's more or less every website should be a JS-powered (or, in the future, web-assembly) SPA without any kind of back-end fallback for user agents that don't support it, thus making JS capability the bar for any UA. That's short-sighted, doesn't consider user conditions outside of a narrow range of experience, doesn't consider that there might be user agents other than browsers as commonly understood. If that's all you have the resources to do and how you choose to spend them, that can still be reasonable engineering (though my experience is the benefits of figuring out how to make it work w/o JS first -- if it's possible -- often pays engineering dividends), but I think it's weird it's the default now.
> Try downloading Firefox 1-10 and see if they work today ;)
Firefox 1-10 would be broken because they're embedded in a set of assumptions about specific non-web platforms, not because many (if not most) websites couldn't reasonably support them as clients. I don't see any reason to import the shortcomings of non-web platforms into the web.
So thanks, but no thanks. There is enough of planned obsolescence already, no need to add another weapon to the arsenal.
Babel can already translate ES2018 async iterators and rest/spread into ES5 code that works pretty much everywhere.