The real reason is in numbers - how many people that could program a PC starting from bootstrap in assembly are out there, and again how many programmers that can paste Java(EE|script)? code together to make something work are out there?
The world needs tons of software, and the vast majority of that software just needs to do some things right some of the time, and an average Java EE developer toiling away in a cubicle is good enough to deliver it.
Writing efficient software is a HARD problem, and it doesn't make economical sense to actually write efficient software, it makes sense to write just good enough software and throw hardware at it. For the price of a developer-year you can provision hundreds of machines to run that piece of code.
The world needs tons of software, and the vast majority of that software just needs to do some things right some of the time, and an average Java EE developer toiling away in a cubicle is good enough to deliver it.
Writing efficient software is a HARD problem, and it doesn't make economical sense to actually write efficient software, it makes sense to write just good enough software and throw hardware at it. For the price of a developer-year you can provision hundreds of machines to run that piece of code.