Well maybe the reason why polkadot didnt conduct bounty campaign before is because they are confident that the project will still become successful even without the help of bounty hunters that will promote thier product.
They have a Good vision of the project and they are confident because of their own effort and knowledge and also sincerity ?
But yeah Polkadot don't need to conduct ICO because look at them now
https://coinmarketcap.com/Sitting at number 6 position and even surpassed Litecoin that shows great movement since november last year.
And also There are so many things i heard about how good this project was and claiming that will reach 100$ this year , but that will be revealed if they can break the Binance position .