Everything depends on what you mean under the key players. It should obviously be the team of the project and product by itself. Good ones will always get their hard cap. No matter how good is their PR team.
Endorsers and advisors for some reason are playing an important role but usually it doesn't influence the product.
Marketing budget (in fiat, not tokens) is the key player of most ICOs
You need to create high hype beyond your project and best advertising tools cann't be payed with your worthless tokens. Thats cost too much money but is the main factor of success
Many ICOs, especialy handelled by beginners are trying to negotiate the token payments for their promotion. Sometimes the good ones are getting lucky and having some good deals. It is not necessary to have fiat budget.