As has been mentioned, many radio amateurs tend to be in the types of fields where various forms of rules are the name of the game. Electricity always behaves the same. So does a computer (assuming it is working correctly, it simply executes one instruction after another; it doesn't deviate or take initiatives of its own). And so on.
However, there is another reason as well which I think is important but that no one has touched on. You point out that:
Most hobbies aren't nearly as strict. If you want to use 80 grit sandpaper instead of 60, or drive 110 instead of 100, no one cares. Absolutely no one would report you to a federal agency for not wearing a mask painting, or using a double instead of an int.
If you use 80 grit sandpaper instead of 60 grit, nobody else is affected.
If you drive above the speed limit, well, others might be affected, or they might not. It depends very much on the situation. (Also note that some countries are very strict about speed limits, including "no speed limit on Autobahn" Germany.)
If you use a
double (floating-point) type variable where an
int (integer) would do just fine, most won't care because most won't (or even won't be able to) realize, and those who do realize will likely know whether it matters or not.
On the flip side, the radio spectrum is constantly under "attack" from different directions. Commercial operators want slices out of the radio spectrum which is allocated, in many cases, on primary basis to amateur radio (that is, other spectrum uses are outright prohibited, or other spectrum users must accept interference from amateur radio stations). Amateur radio licenses are not handed out to anyone who asks and pays; an amateur radio license is a privilege that comes after proving your ability to handle the rights that come with it. (Basically no other radio spectrum users get to use homebrew equipment, decide on their own the transmission mode, transmission bandwidth, exact frequency, transmitter location, etc.; for just about every radio service except amateur radio, such things are stated in the permit document. Amateur radio operators have a huge amount of leeway in this regard.) Part of that is proving your knowledge of relevant regulations, radio theory, and operating practice; the exact examinations vary by country, but they cover largely the same subject areas.
What amateur radio does have, is very generally written regulations which sets the boundaries for how we (amateur radio licensees) are allowed to use the spectrum. (One of those boundaries is that amateur radio is non-commercial in nature.)
A commonly held opinion is that if we in general start accepting people going outside of those already very permissive regulations, the commercial operators in particular will be able to point toward that practice and use that as an argument for taking over portions of the spectrum that is currently allocated to amateur radio. Some of that spectrum could easily be quite valuable to commercial entities, and much of it is allocated on a primary or shared-primary basis to amateur radio.
By asking of each other to strictly adhere to the rules that do exist, we reduce the risk of commercial entities being able to point to rampant rules violations as an argument for reducing the freedom of and spectrum allocations to radio amateurs.