Of course a share value can fall. But it can't really fall while the company is still okay. It represents ownership.
What ownership? Can you go and require some real assets of the company? No, its just the paper that allows you to get money according to the market price. The stock price is much higher than the real price of the company assets. And tomorrow your company may be ok, but the price will fall. Or the company will default on its debt and you will not get anything, only your paper as a souvenir.
A coin on the other hand? A coin can go to zero while the company is fine. Why should the company care?
The problem with a coin is that there's nothing to prevent the company from just plain walking away. It got the ICO investors' money, it owes them nothing, so... done deal, right? It's over. The company gets nothing for whatever resources it devotes to the ICO coin after that point, so sooner or later it's just going to cut expenses and drop it.
Maybe it should be clarified in the smart contract? Sometimes, for example, the team tokens blocked for a certain period of time. In theory, this should affect the activity of the company. But its not enough. We need more restrictions, that will help maintain the price and will persuade to take care of the results of the company. Maybe, raised funds should be blocked too, and must spend through the smart contract. Maybe there are should be some other restriction or features.