Not the OP, but I assume they mean that it sends things like the other players' locations, which can be found by cheaters to be seen with map hacks and such.
It got a little better a while ago, where they only distribute player locations to clients that have to be aware of that player due to either line of sight or being able to hear them. Faceit has a more aggressive system where player locations are only sent once you see them, which sometimes, in high-latency scenarios mean you suddenly see then appear somewhere without having them seen moving there. It's all a trade-off, I guess.
Doesn't this also mess with tactics such as being able to hear someone coming? I don't play CS:GO, but I do play Enemy Territory (id Software, 2003) and hearing when an enemy is coming is a crucial part of being able to get the first shot and kill someone.
Of course you could expand the limit of when to send data to the point where you can hear someone, but that wouldn't defeat short-range wallhacking, which is just about the only kind of wallhacking that's useful.