Maybe they just don't want to trust again. Scared to entrust again their hard earned money to professional scammers such as the ICO's own "reliable" team. Needless to say, it was an experience that was very frustrating and not that easy to cope with.
"I've participated in one ICO sometime ago and at the start it looked very promising. The ICO's very own chairman along with the admins were just so overwhelmingly accommodating to every investor and bounty participants as well. Always available in the telegram channel to answer all the inquiries. Nonetheless, when it was time to give back the investors their rewards and benefits, they were all gone. Taking with them all the investors money".
So i guess, for some investors, they just wouldn't want to go through with that same situation again.