All cars were loud and belching unburned hydrocarbons 40 years ago. Comparing motorcycles to modern cars is missing the gains in street life impact that have actually been made.
I really wish the standard penalty for that would be "you lose your motorcycle license for 5+ years and the motorcycle is crushed into a cube before your eyes". Not "here's a 100 EUR fine and you have to undo the modifications, show us that you did it, and then put them back on".
It's completely unnecessary, hard to do accidentally, and a great way for one single person to affect thousands of others in a single day.
Motorcycles are probably the main offenders but some cars, trucks, and even 2-stroke gas scooters can be ridiculously loud. The law should not discriminate.
Also, ebikes are awesome alternatives to motor scooters. I've built one for a very low price not too long ago, it was very fun.