I think it has to do with the connotation attached to gambling and gambling addiction plus Money laundering etc.   Bitcoin mixing and online gambling are often associated with illegal activities such as money laundering and gambling addiction, which is why they have a negative connotation in the Bitcoin community, even though not all Bitcoin mixing and online gambling services are used for illegal purposes.

As for exchanges, exchanges are not inherently considered bad actors in the Bitcoin community. though there have been instances of centralized exchanges being hacked or engaging in fraudulent activities, which has led to the loss of user funds. but inherently not considered bad actors. thanks