I hazard a guess you aren't a web-developer. Imagine that for every fix, new features and improvement to your platform of choice you can't use it until 95% of your audience has the ability and incentive to upgrade.
Fair point, but still nothing compared to OS development, where you usually can't release a new version without having to worry about people trying to run it on 10 year old computers and everyone expecting entrenched, old enterprise software that uses all APIs you wish you could deprecate to continue working flawlessly.
A lot of developers can't have the luxury of using the latest and greatest tech because they have to worry about existing customers. They can't start from scratch without upending existing revenue streams.