Yes that's quite a good observation and there is a logic too behind it. Altcoins have a market swing only when there is not much happening to bitcoins but when the bitcoin market is on a swing everyone trades bitcoins and hence the price goes down for altcoins.

I am quite sure that the price of altcoins does not bother anyone since they cal sell for btc and the btc price has already increased means they still hold same value of USD or even more.