Now people trust anyone no longer. ;)Therefore, it takes more time to convince people of the plausibility of a project and its future goals.
I don't know what you are talking about. The ICO's are all expecting people to invest in a coin for a long period and then they release the coin at less than 60% of the ICO price. It's not fair for most investors.
I think the icos last for a long period of time because the longer the program lasts, the more investors they can get. When talking about the rewards, I think it also depends on the icos if they give more rewards when their icos last long.