Because even though they can, that's not what they're doing.
I see comments like yours on this site pretty often, and it is tiring. There are many reasons people behave the way they do, and probably the most common reason is that their behaviors haven't caused them any harm as far as they know.
The warning "Read and change all your data on the websites you visit" is perhaps scary the first time you see it, but then it becomes insignificant as time goes by and as extensions get installed without causing any visible harm.
> The warning […] is perhaps scary the first time you see it, but then it becomes insignificant as time goes by…
Which is exactly why it's dangerous. Granting access like this without a thought to the potential consequences is just asking for a bad character to take advantage of the blind trust people place in extension authors.
The core issue is the options Chrome gives extension authors. Offering the ability to grant permissions per-site and per-use would greatly reduce the threat. Even just a per-use "Are you sure?" confirmation would help.
> The warning "Read and change all your data on the websites you visit" is perhaps scary the first time you see it, but then it becomes insignificant as time goes by and as extensions get installed without causing any visible harm.
LOL, what matters is the threat itself and not your waning level of apprehension over the threat. This is really a very, very strange comment. The point is there is no need for this to be a browser extension. Putting an input element and some AJAX on the page is trivial, so I really don't buy the excuse that they haven't had time to put together a web app yet.
I see comments like yours on this site pretty often, and it is tiring. There are many reasons people behave the way they do, and probably the most common reason is that their behaviors haven't caused them any harm as far as they know.
The warning "Read and change all your data on the websites you visit" is perhaps scary the first time you see it, but then it becomes insignificant as time goes by and as extensions get installed without causing any visible harm.