https://www.youtube.com/watch?v=wFr1ooaVPjY&list=PLDt0J62yU45vZ15bdGAmZuuyuLtd-MCxc
Why is it there are cryptocurrencies with no ICO?
For several reasons, one being that before Ethereum it wasn't possible to launch a crypto token very easily. You would of had to launch your OWN coin on your own blockchain and have developers manage the chain and have miners support it, with ethereum anyone with a little bit of solidity knowledge could launch their own ICO token
The second reason I think is that because ICO tokens are or could be seen as a security, since most of them have companies behind them they fit the criteria Jay Clayton talks about above. Also in the traditional sense of crypto, ICOs are not a fair form of distribution. Take Bitcoin for example, there was no initial offering, everyone had the same chance to mine it or buy it, there was no exclusive rights to whales to buy it at a cheaper price like some of these ICOs run.
I would bet that 99% of bitcoin maximalist believe all ICOs are scams, some go so far as to say smart contracts themselves have no use.
The advantage is clearly that you can get a butt load of capital right off the bat but some of the disadvantages are probably being seen as a security and or the product/idea failing. Hope you found my answer helpful.