First of all, remember that you're comparing photons (transmitted EM) to electrons (the power grid). This is important.
Allow me to use a couple of metaphors
When drawing power from an electrical grid, it's like drawing water out of a swimming pool. The individual pipe may draw very little water, and the result may be hard to detect, but the volume of water in the pool is decreased by the pipe no matter where the pipe is.
But that doesn't easily reflect how EM transmission works. A radio receiver is not drawing energy out of a pool (kinda, I'll get to that). Imagine, instead, a balloon being inflated. The "receiver" is a point on the balloon that's enjoying the benefit of the portion of energy that one point receives as the whole balloon expands. The fact that the single point enjoys that bit of the whole doesn't impact any other point on the surface of the balloon enjoying their portion of the energy needed to inflate the balloon.
Setting aside the metaphors
When a transmitter sends out energy, the energy delivered to the antenna is the rating (e.g., 50 kw). That energy expands away from the antenna (simplifying things a lot) in all directions - and each little point along the sphere of that expansion carries a portion of the 50 kw energy. The receiver captures that little amount — which has no impact on your next door neighbor because they're getting their little amount at a different point along the surface of the expansion.
Thus, it doesn't matter (again, really simplistically) how many receivers there are. They all capture their little portion.
Where you can get into trouble is when two receivers are too close together, interfering with the ability to capture the energy from just one point along the expansion. This is because receivers are not infinitely small — but that's another story.
Yeah, but when I think about those metaphors, they don't really work, do they?
Of course not. That's the problem with metaphors. What you're not realizing is that you can't compare photons to electrons. You can, e.g., draw an electron away by providing a lower-resistance path, thereby robbing your neighbor of electricity. But you can't draw a photon away like that. It's basically going in a straight line from the transmitting antenna until it hits something it can't move through — like a receiving antenna.