Because they are generally not a threat. Certainly they are a manageable one with even a modicum of effort.
Sorry to say, but your postings in this thread suggest that you can never forgive a snake for taking your pet and now every snake is a "threat."
Snakes can be threats, but not just be virtue of being a snake.
What's the difference between an armed thug invading my home and and hunter in the woods? Both are armed and are equally "threats" so I should kill them both dead?
The ability to reason and see nuance is what separates humans from animals.
Tarantulas are venomous, and their venom can cause pain and other reactions in people. Their venom isn't as dangerous as some old horror movies portray, though.
You're right, although their venom wouldn't be lethal.
Apparently a black widow's venom isn't either but the aftereffects are very unpleasant.
As an aside, how many here know that a venomous snake can deliver what's called a dry bite?
This is a strike releasing little or no venom and is mainly a defensive action.
The snake is trying to warn you away as it tries to get away from you.