Because it's designed as a service, and I mentioned in my list of things to look for that this is undesirable, in my opinion. I also was unable to gather enough technical information on the currency to determine if it can serve a very large user base. I'm not saying Steem won't grow, I just don't think Steem's designed purpose is to replace BitCoin as the mainstream currency of the world... It also does not have a desktop lightwallet, which is important for security reasons, and the marketing does not seem to be as good as the one for my top 2 picks, at least.