In actual reasons vary from person to person for one person it may be the hobby to create a place in every field that why he is making a coin in the cryptocurrency market , there may be chances that few people want to create a better market with the same Technology that is running since old time .
And few people make altcoin just to make money , in the present time to scam people by creating ICO is a very simple method , digest launch AI with better market advertisement and after that many people get attracted toward the ICO project to make investment and that results into a big collection of amount of money for the coin token creator .
And then they launch their token in form of going at any exchange which is  worst , are there remain very low volume . in this way they make a big amount of money for their pocket and after that they get back in I should project again with another name with the same coin Technology as you said copy paste of coins .
well here I would like to suggest you that keep yourself away from the investment of ICO or if you want invest your money in ICO then you should be sure that you are not going for the investment blindly without investigation or Just by suggestion by anyone you should make analysis yourself and make sure whether project is looking genuine or not .