Why not put an active listening device in your bank card? Why not secretly sew it into your clothes.

I'm not saying there can't be one in the remote, it's just that the TV itself is a much better option; always has power, doesn't rely on chemical batteries, doesn't need to maximize battery life, (typically) placed with open facing to a room (for clear and consistent audio.

Sure, you can put an always-on listening device on the remote, but you're gonna use more battery to power it, you're gonna need more hardware to handle communication to the TV, and more battery to power that. It's a pretty big compromise for a device that is supposed to go years without changing the batteries. All that trouble to put one in the remote when you can/probably have one in the TV already, and then then remote gets stuck in the couch cushions, or put in a drawer, or lost, or replaced with a different remote. It just doesn't make sense to me to put that kind of effort into what will inevitably be an unreliable and inconsistent spying device.