I think the answer to this question deserves a two way explanation;

1. it may be that they never got enough investor to invest in their project during their ICO and they have to discontinue the project.

2. it could be that some persons only floated their projects to make away with investors funds. it is not far fetched from the truth that some projects are scam as they lack foresight to make an indelible mark in the cryptosystem.

I will therefore advice we always read about their team of contributors and google their profile to ascertain their proficiency in the crypto business alongside. Accessing their whitepapers to ascertain the relevance of the project to societal demands  is another way of knowing if the project could succeed or fail as investors themselves wouldn't want to invest in a project that will have no economic relevance.

Honestly with the high level of suspicion, no investor would want to be scammed; therefore adhering to this aforementioned reasons could help us to know why projects either fail or are discontinued, thanks.