I guess the hype is very important, it is harder to gain followers from 50 to 51 but it is quite easy to gain that from 15000 to 15001. Hence the bigger the hype the bigger the follower count gets. It is quite easier to gain 10% when you already have 100 thousand followers but quite difficult when you have 10 people interested.

After you pass the initial troubles of getting bigger you gain a lot of followers. For that reason a lot of ICO spend money from their pockets to give ads on facebook, instagram and mainly google (and some even spend money on bitcoin ad networks). If you can put your name and your coin in front of millions of people by spending thousands of dollars, you can actually make that money back from the ICO funding. Of course, it is important to note that when you spend that much money, there is always a risk of losing it in the end without any interest to it.