Yes, the axiom fits pretty nicely here: "Jack of all trades, master of none." It's extremely rare to find someone who is a master of all, can keep on top of current tech (in all domains), etc. Web development is becoming like the medical profession, where every single subfield is specialized. Yes, there are people who can do that, but they are far and few between. Most back end devs are typically not visually creative types like are typically needed for the front end, and vice versa. How many good back end devs are also good graphic artists and at layout (beyond adding a background image to bootstrap)? How many front end devs are good with SQL?