With the explosion of new wireless electronics, radio frequency interference is everywhere. Keeping it out of a province-wide system with dozens of repeaters is nearly impossible. The best way to reduce interfering signals is to move to implementing CTCSS tones on the repeaters. I've noticed several repeaters in my area recently adding tone requirements. Repeaters often operate in environments with lots of interference - spurious signals could cause the repeater to activate, but requiring a sub-audible tone ensures it only responds to legitimate signals.

Another reason is preventing interference from other repeaters using the same frequency pair - long-distance propagation can cause co-channel issues, but different CTCSS tones prevent this. It's really about keeping systems clean and functional.

With the rise in repeater numbers, channels have to be re-used frequently, so it's possible for a station to access more than one repeater at once - CTCSS was introduced to overcome this problem. Makes perfect sense from a coordination standpoint.

I've seen this trend too, especially on linked systems. Stray signals key up repeaters causing noise that gets retransmitted to all other repeaters, interfering with normal use. CTCSS really helps maintain network integrity for emergency communications.