Reason number one:For pump&dump purposes.
Reason number two:Exit scam ICO(which is kinda like the first one,but with pump&dump they could pump the coin again and gain aditional profits).
Those are the real reasons.The fake reasons include:instant and cheaper transactions,easy and profitable mining,technology innovation that will beat the crypto competition.
It is sad, but true. Most coins are created so that their developers can benefit financially. We just have to look at all the coins which are considered "dead". Their developers have most probably profited at the expense of ordinary investors.