@richcg provided us with a fairly nice explanation in a recent post that can be found here:
https://steemit.com/bitshares/@richcg/bitshares-got-a-c-in-the-weiss-cyrptocurrency-report-i-believe-this-is-good-news
So why did Bitshares get a C+ and not an B or an A?
Here is why I think that Bitshares got a C+, and rightly so. First off, Weiss’ index measures market bias and public acceptance. And as we all know, this is one area Bitshares is heavily lacking. We need a stronger brand and market penetration. The second factor that has hurt Bitshares’ grade and most all cryptos is price fluctuation over time. At one point Bitshares' price went from $0.46 down to $0.05, and recently its price went up all the way to around $0.90 and back down to $0.24. This in their eyes makes Bitshares a bit risky for investors. Remember that one of their main goals is to protect investors.
If Bitshares can improve on these two metrics before Weiss’ next report comes out, we can be sure to see the grade improve from a C+ to a B or even a B+. Why do I say that? Because Bitshares scores high on all other metrics such as speed, scalability, security, and decentralization. Very important factors indeed.