Teemo's shroom's life total

Is there a reason that teemo shrooms have so much life? I was playing top lane vs a teemo yesterday, so I got a sweeper instead of ward trinket. When he hit 6 and started dropping mushrooms in front of his turret, I did a sweep. There were 2 shrooms there.

I could not even kill one before the vision expired. I hit it 3 times.

If I can see it, I should be able to 1-shot it. They aren't hit by aoe, so there really is not a reason for them to be sturdy. If a player manages to detect a mushroom before it goes off, that player should be rewarded by being able to kill it.