> Sure you can - you just do it. You just make the necessary fix.

No, you can't. Not simply.

> But you do it quickly, within a short time of launching it. Anyone who was able to make use of it within a couple months, will be able to adapt and fix things.

That's not how the web works. "People who make use of it in a few months" could easily apps and sites serving millions of people. This is a process that applies not only to image codecs, but to, say hardware APIs and interfaces, network protocols etc.

> But there's no reason to take so long.

There are very many reasons from technical to political to anything in between (and sideways, too).