Using /kill @e command too many times causes mobs to stop spawning

i have been using command blocks to kill specific mobs around my base but now all of the sudden nothing is spawning anywhere. The command used was /kill @e [type=mob name] without a specified radius. I noticed that at first mobs would die when I approached them but eventually they just stopped spawning all together. I had the command blocks set to repeat but connected to a pressure plate.