Why don't amplifier Companies use high end fuses?

"Because they know better and are technicians "
Well what I do know is that engineers and technicians often talk rubbish, and have ears that demonstrate that their ears seem to be pointless.
And if anyone writes that studios have kit a or b so must be good, then that is even more rubbish. If they knew more than not a lot, there would not be so many bad recordings out there.
But back to the original issue, I recently bought a ps audio power regenerator which came with a stock power cable, and the instructions stated that although a stock power cable was included, they recommended "better" ones should be used as they would improve the quality. So an item that cost rrp around £2,900 uses a cord that cost £2 and comes with a recommendation!? As said above, it seems to be a marketing decision as to what to include or not.

Paul McGowan is very transparent about the power cord issue.  He, like the vast majority of audio entrepreneurs, brings gear to market at a specific price point.  He includes a good, heavy gauge power cord with his regenerators but notes that upgrading from that cable can improve the performance of his gear.  Additionally, Paul endorses his customers to use resonance/vibration control devices with his regenerators and other gear to further enhance performance

Paul McGowan is also a proponent of aftermarket fuses, to bring this full circle, and supplies some sort of fancy fuse in some of his gear.

When I auditioned a pair of Odyssey Audio monoblocks, in my home, I had occasion to remove the covers(with Klaus’s permission). Apparently, Mr Bunge(electronic designer and manufacturer) believes fuses make a difference, given the amps had all the fuse holders(mains and rails) stuffed with HIFI Tuning’s products. Don’t know if he sells them equipped that way though.

That's what you're impressed with? Did you even read the specs on that stuff? I'm looking at the Stratos Mono. They claim 120 amp current delivery. Through 6.3 amp fuses? With a 400VA transformer? Not for very long if at all! To sustain the kind of current output would mean rail voltages sagging to 3.2V. He's calling it out as 180 watts into 8 ohm. That suggests he's running 32V secondaries off the transformer for rectified 40V rails. That figures out to 4.74 amp. To keep the 6.3 amp fuses from popping at 2 ohm means it'll only put 79 watts on the outputs. 

Here's the bottom line. That amp is built to a budget, most obviously. It couldn't have cost much more that $500-600 to build. It seems to me to be pretty ridiculous to spend 10-20% of the build budget on fuses when that same money would buy a much larger transformer which would make a vastly more meaningful difference. It's very likely that the fuses make a difference because that's the exact kind of anemic power supply that would be prone to minor perturbations. I know I've said this many times before. 

For comparison, my little home brew amp is 31wpc and has a 600VA toroidal with 24V secondaries for 32V DC and it will drive 300 watts into a 2 ohm load without a hiccup.