Why not, I keep all my trading capital in btc or most of the time in stable coin, bitcoin controls the market and no matter the coin you leave your trading capital in, you might still acquire some loss if the price of bitcoin dumps, so I leave my coin in bitcoin anyways, though I didn't say everyone must leave their coin in btc, I am leaving it their because that's the choice I have made, every trader can make their own choice on where they want to leave their trading capital and no one would say anything about it since it's their choice to make.
BTC is simply a more reliable cryptocurrency, the leader. Meanwhile, I hold the other altcoins as well. For instance, Ethereum is supposed to pump - why not keep it for a long time?