People gamble on alts (99% of atcoins are worth 0) when BTC is boring and its hard to trade it. When its stuck in consolidation for weeks.
Furthermore, when Bitcoin do 30% to 60% positively in a few days or couple of weeks, altcoins will drop in BTC values. You can not trade altcoins profitably if you long them.
There is no need of trading altcoins when btc do +60% in 20 days. People simply trade BTC.
Trade Bitcoin or hold it and try to take profit before you switch to altcoins.
But as soon as BTC will stop a little money will flow to alts creating new alt seazon. I think that sooner or later alts will reach new ATH and yell better return than BTC. The only next alt seazon killer would be BTC rally stop with -30% red 1 day dildo.
The altcoin season is the last thing to happen in any market wave. After an altcoin season, the market will be corrected and it will need a few months to have a new big season in bull run. In bear market, we will have to wait one to two years to go through a winter season.