Altcoin seasons are driven by speculation and hype, nothing more, when you see the price of bitcoin going up for the most part there is a fundamental reason for it to happen, in 2017 it was because the segwit update was finally implemented despite the opposition of the miners, and the current rally is being impulsed by institutional investors coming to the market because they are losing trust in fiat currencies, but altcoin seasons happen just because of speculation and they can happen while there is a bitcoin bull run but they can also begin on their own when a new way to get money or a supposedly new technology emerges.
Please allow me to repeat with small edit "Altcoin or bitcoin seasons "are driven by speculation and hype", more correct to generalize it as that. People in the market have different types: investors, speculators, traders and they all want to get more money back from their initial capital.
Ridiculously, the market don't mind who are in the market and what they want to do in or earn from a market. It only operates with its own rule (that can be manipulated) and redistribute the wealth (the capital) from the most to the least members. It is true for any financial market (stocks, real estates, gold, crypto market).
There is capital flow in the crypto market and it switches periodically from bitcoin to altcoins and altcoins will have their seasons. In middle of 2019, there was a season for DeFi tokens (they are altcoins but are new altcoins). I am waiting for another season for old altcoins in 2021.