[drewmclellan]

Testing in different browsers is a real pain. Getting front end code working properly in all those different browsers is even more of a pain. Getting that code working really well is harder still.

It takes time, dedication, skill, and a lot of specialist knowledge of bugs, quirks, standards and tools.

That's the reason that front end development is a role in its own right, and not just a function of someone else's role.