Really the number one reason they and people like them use suppressors is for hearing protection. They're operating in urban areas, maybe even going in small rooms, extra hearing protection is important. It also protects nearby civilians ears, who wouldn't have extra hearing protection, police have been sued for hearing damage thanks to loud weapons before.

It's also to just reduce disturbances, with a suppressor fewer people will hear gunshots, and so fewer random civilians will call 911 and cause issues. It's like how emergency services won't run their sirens when they don't need them right then (like if the road is already clear, or it's night-time), just their lights.

Suppressors don't make it completely silent, they just make the noise a lot more manageable and reasonable. They generally aren't really used as sneaky spy tools, though sneaky spies might use them (along with subsonic rounds and modified firearms). Suppressors are actually a really good safety tools, and it's a really good idea to have one as a gun owner. It protects ears at the range, and god forbid you ever have to actually use a gun, a suppressor would probably be the only hearing protection you get.