There are multiple causes for this ...
1. Some legit ICOs can use KYC to reduce the number of fake accounts trying to benefit their "generosity".
2. Some not-sure-if-legit-probably-no will sell the KYC info to the highest bidder.
3. Some bounty managers may use KYC to not pay for some work done.
All in all, since the ICO/bounty/airdrop is made my people you don't know and you are not sure about their intentions, it's safer to not give out your info so easy, since you may have nasty surprises later on.
Even if you'll lose a couple of easy bucks because of that.
I understand that KYC required by bounty campaigns are reducing number of participants (fake and but also real participants) and that cause that ICOs dont have to send all allocated bounty tokens.
But I do not understand why ICOs want to reduce fake accounts, I thought that they need as many investors as possible to collect enough money for their projects.