Most of the price from Altcoin drops when the Bitcoin price drops, and as the bitcoin price rises again, Altcoin's price will rise again slowly. It happens because almost everyone who owns Altcoin will sell their coin when Bitcoin price goes down, and will buy again when the bitcoin price goes up again
You are spot on with this observation. When bitcoin prices dropped from $18000 to $7000, all the alt coins went in red. Some even completely collapsed due to such a big crash. I think that people simply associate crypto with bitcoins. When I say to my friends that I am investing money in crypto, they simply assume that I am investing in bitcoins. Many of them do not even know that other alt coins even exist. The reason for bitcoin prices affecting alt coins prices is that most of the alt coins are traded with bitcoins only.