Temperature is only one facet of the total energy state and is simply insufficient on its own to get the job done. I know, we thought the same thing and burned the crap out of ourselves in the shower.

We can't alter the universe's laws for our convenience - we tried, doesn't work. :)

And from the universe's perspective, a temperature scale that's built off a particular kind of matter within a certain range that's convenient for weird ape-people on a specific planet on a specific star is no way to run an entire universe.