Why shouldn't there a one size-fits-all type language? To the un-initiated (i.e me), this makes sense: one for mobile devices (java), one for the web (PHP?), o

Why shouldn't there a one size-fits-all type language? To the un-initiated (i.e me), this makes sense: one for mobile devices (java), one for the web (PHP?), one for UIs (javascript) and one for low-level work (c/asm). How can someone who makes a living writing code be expected to keep up with the trend that @madhouse talks about?