Have you heard the tragedy of Internet Explorer 6?
It is said that this browser was so good, so ahead of the others from his time, that he achieved the power to... monopolize the entire web stack. Ultimately achieving 95% market share, websites for a while didn't bother to support other browsers.
However, time passed. IE6 got old and other browsers got progressively better. Suddenly, IE6 that was so good (compared to the 5.1 and 5.5 era and its competitors) was not so hot anymore.
So, we transitioned to the better browsers, right? Wrong! Companies that homologated IE6 took almost a decade to transition. Devs took almost a decade to cultivate a workable cross-browser culture. There was a particular dark era that required you to support 3 or 4 different IE versions (6 through 10), each one with its own quirks.
So, yeah. Anyone who lived through that era will never, ever, support a single browser implementation. It is a deep trauma. We want browsers to get their shit together, so huge gaps like that will not happen again.
