Because they just don't work the same way, it's not possible. Computers have components with cores the generate heat in a specific spot then are wicked away by heat sinks and either cooled by liquid or a fan. We're talking about solid state circuitry that generates heat due to processing load. There's not really anything in an amp you can put a heat sink on to wick away heat. At least not in a tube amp. Plus I don't know many people that would want liquid running through their amp. Or having a to run like a fish tank pump. lol. Liquid cooling systems for computers are also completely unnecessary and most people don't realize you have to have a water pump and cooling tower outside the case in most examples for it to function.