The problem is that most of the regulations only cover vehicles used on public roadways (at least in the US). Most of these parts will say that they are for "off-road use only", which make it hard to go after the manufacturer or installer.
We would need to change the laws to say that the requirements apply to any vehicle manufactured for use on public roadways. Some of the requirements need to be changed from just applying during design/manufacturing to at all times so the majority of the loopholes currently used can be closed.
What makes it harder is that many of these exhaust systems are used off road only, on dedicated track bikes. You can get a street legal supersport bike for $10-15k new, and with bikes that powerful, changing from a street legal to performance optimized exhaust can make a significant difference. But these supersports are also often used on the streets, just like you see people driving Lamborghinis and Ferraris on the streets (but not often because fast cars are very expensive). Just another thing which makes legislation harder.
We would need to change the laws to say that the requirements apply to any vehicle manufactured for use on public roadways. Some of the requirements need to be changed from just applying during design/manufacturing to at all times so the majority of the loopholes currently used can be closed.