My impression (formed from growing up as the annoying kid in the datacenter back when they let annoying kids hang out in the datacenter) is that buying new supercomputer hardware takes takes a lot of money and a really long time. Showing a return for the big investment might take much longer than the life of a typical PC.
Once the a computer is actually in place (especially in a University setting), the interesting work begins, trying to write the best code for it and even improve the existing algorithms.
It seems like there are computer purchases motivated by "this machine will run our existing code faster" and those motivated by "this machine will allow us to write code for it that will prove something faster". A supercomputer seems, almost by definition, the latter.
Once the a computer is actually in place (especially in a University setting), the interesting work begins, trying to write the best code for it and even improve the existing algorithms.
It seems like there are computer purchases motivated by "this machine will run our existing code faster" and those motivated by "this machine will allow us to write code for it that will prove something faster". A supercomputer seems, almost by definition, the latter.