Why are water cooling kets...

Why are for the most part all weak the only one I would ever buy and may buy in the future along with a costom one is the koolance and I would probebly mod it with bigger fans or some thing. Why does a company just not make a super good one.
O and can you use any water block with the Koolance for a 478.

I have a zalman block on my 2.0a @ 2.8 with a exos.