It's because the cost of detection is bullshit <_<
Dots:
Kappa Life Detector: 200gold, 1600 sight range, 1000 true sight. Lasts 3 minutes. 2 charges
Tengu Spy Camera: 200gold, 900 sight range, 900 true sight. Lasts 3 minutes, placeable only on trees(they cannot be destroyed by any means). 2 charges.
Baby Tengu: 750gold, 1000 true sight range, drops on death.
Dota:
Sentry Ward: 200gold, 70 sight range, 950 true sight. Lasts 3 minutes. 2 charges.
Dust of Appearance: 180gold, all enemies within 1050 range gets revealed for 12 seconds. 2 charges.
Gem of true sight: 700 gold, 1100 true sight range, drops on death.
It's about as costly as it is in dota, and earning money is probably a lot easier in dots than dota. Wriggle is basically Rikimaru with a +100+(lvlx10) physical attack that silences instead of 120+agility damage, more invisibility, and no slow/long silence but instead gets additional attack(bugs) that heal her for 40% damage of each bug at the end. Which in a typical case scenario, about 300.
As for where I'm going with this... It's pretty similar to deal with Wriggle in dots as it is in dota and Rikimaru. If you don't buy wards, have an tanker ally with a gem/true sight ability, then yes, you will rage.