I guess it is because there are lots more issues related to Altcoins than Bitcoin which thoroughly affect the whole Altcoin market as a whole. Whenever there is a big news in relation to altcoin the whole market is being affected maybe due to the generalization brought by the recent happenings which involves Altcoins which is I think until right now is still not into good condition to regain the trust of the investors. People do obtain or trust more into Bitcoin undoubtedly because it is well-known to be the safest and the most secure cryptocurrency existing in the market that is people chooses it more over Altcoins. With such reasoning people do have in their minds towards Altcoins, it makes the prices of all Altcoins whether it is good or bad project to be affected on this making the whole Altcoin market to be fragile compared to Bitcoin alone.