The reason this is true is simply because it's dominant, so every site builds for compatibility for Chrome. This is similar to how Windows is the best OS for gaming. Not because Windows has any technical advantage, but it's simply what developers build for. Firefox would "be the best browser" if it were dominant.
And I remember a time where it wasn't dominant, where people went out of their way to install it, even when their OS would shove other browsers in their face...
It didn't become dominant by being a bad browser...
You mean, when Google went out of his way to make people install it. It is delusional to believe that the average PC user installed Chrome for its technical merit. They installed Chrome because there were advertisements everywhere, from subway to Youtube, and, above all IMHO, because ‶the Internet (understand google.com) said I have to install Chrome to go fast″. And that's not counting the heaps of installs that must have come from Chrome being bundled in adware installers and sneakily setting itself as the default browser.
Just go ask people from you family using Chrome why they do so, I bet at least half of them are not even aware they are using Chrome and not just ‶going on Google″.
That is, pretty much every tech person I know switched to Chrome because it was just so much better than what existed at the time, primarily its faster JS speed with v8, and I think most importantly for actual end-user experience, per-process tab isolation so that one bad tab wouldn't crash the whole browser. These were real, important innovations that had the tech elite quickly adopting Chrome.
So what happens once it's adopted by the tech elite? First, they push for making it the default install on new computers, which has a huge effect. Next, every time Mom or Dad or Grandma asks kid/grandkid for tech support, the first thing they do is say "Install Chrome first, that should help with a lot of your problems" - I certainly know I did it with my family members.
So while I don't want to discount advertising, I also like to say that it's easy to advertise great products - you just need to let people know the product exists, because eventually the product's benefits are self-apparent.
To bring my own experience to it, I stuck with Firefox all throughout that period and never had significant bugs, slowdowns or crashes. Though I will admit that there was a period when Chrome felt noticeably smoother.
IE6: hold my beer
It just stagnated and became the worst browser over time