Exchange or gambling businesses seem to know already the account characteristics of someone involved in illegal activity so the owners of these businesses may have started to suspect the movements of the perpetrators of the illegal activity. Business owners will immediately ask them to do KYC to find out the background of the account owner. And if they are suspected of having anything to do with illegal activity, they can immediately report the results to the government.
Truly the government is always on the track of account holders and you know they know themselves but one thing I believe is that the government knows all the money launderers in their various countries, they know those who indulge in nefarious act and would not go after them but are ready to trouble these organisations such as casinos, exchanges etc just to get revenue from them all in the name of keeping track of account holders. Even the casino owners knows this too. They know accounts of money launderers and others but sometimes they just disguise themselves and pretend not to know as to get their pockets.
However, it is also true that some individuals or organizations probably try to evade detection, making it challenging for authorities to catch every offender, and the government agencies prioritize some targets over others due to resource constraints, it does not necessarily imply that they condone illegal behavior. The focus on certain sectors like casinos and exchanges may be due to their susceptibility to being used as conduits for money laundering.