"Apple's recommended setting of 100 ms advertising interval with a coin cell battery provides for 1–3 months of life, which increases to 2–3 years as advertising interval is increased to 900 ms."
iPhone's have about at 10X larger batter than that. So iPhones can do this for ~20-30 years if configured correctly.
It is not about BLE beacons. Right, they are energy efficient. But receiving party needs to listen constantly and proces these messages. With 1000 beacons around at 1s interval it means the intermediary node needs to send 1000 notifications per second to Apple. That can be buffered and optimized, but still it is some non-trivial number and possible bottleneck to be exploited.
iPhone's have about at 10X larger batter than that. So iPhones can do this for ~20-30 years if configured correctly.