I disagree that it's an issue of simply not working hard enough. The reality is that it's an issue of opportunity costs: There are only so many hours in a day, and every hour you spend on backwards compatibility is an hour that could have been spent on something else. Naturally, as time passes and the older browsers get older (i.e. less popular and harder to develop for), people are going to see less value in supporting then in lieu of the alternative ways they can spend their development efforts.