Nevertheless, if you look at the dollar/robust coin pairs, you will see a steady increase in price (ETH, LTC and dash for example), which translate in stron community support. Moreover, those altcoins are quite useful indeed for the overall environment.
The BTC/altcoin correlation is misleading and cannot be used as a measure of value by itself. One should also pay attention to the fiat/altcoin evolution because that is also very important and the communities supporting the altcoins pay close attention to both factors.
Many altcoins are being dumped because a significant portion of of those holding them were just waiting for a chance to make a quick buck and are not true supporters of the coin.
A strong community won't dump a coin only because BTC is skyrocketing. And when we talk about modern implementations, with PoS 3, masternodes and a strong dev team, the coin will thrive while others are just dumped.
Take a look at DMD's last month performance in these harsh times:
Breaking records! Why? Because we believe in it, we don't dump. We don't care for the BTC forks, our diamonds are a safer bet.