Because the community is the most important aspect of an ICO's success. They give value to coin by increasing the demand. And when the demand is high, of course the price also increases. For example You can see  how big the community of one project  is in their telegram group, but you also need to be careful because some members in telegram groups are made of bots they create dummy accounts to increase the number of members in their telegram, that 90% of the members in their group are just fake.  Be careful and always observe and check if they are really real people who support the project.