The picture shows the price dynamics of the main coins (LTC, ETH, EOS, ZEC, etc.) to bitcoin. You need to look upside down. The chart is growing - this is a fall in altos, the chart is plummeting down - these are alt-seasons.
Dips in the purple rectangles are the alt seasons in the second and fourth quarter of 2017. This is followed by a downtrend period, which is highlighted in red. The good news: we have not yet seen full-fledged alt-seasons on the current bitcoin bullna. The small price spikes this year are a rehearsal.
Why do I suddenly have such confidence? It will be possible to explain in detail tomorrow in a separate post. In the meantime, pay attention to how, starting in 2017, altcoins began to move in exactly the same way, as if it were one index.
The growth of Bitcoin inevitably attracts the attention of random people. With each new cycle, this attention becomes stronger. More attention -> more newcomers to exchanges. The owners of exchanges themselves are well aware of this and monitor the growth of traffic on their sites. As soon as the flow of fresh blood reaches the desired level, the long-awaited viola season begins.
The alt season is beneficial to everyone except beginners. Exchanges sell their stocks of coins at inflated prices, because inexperienced players are ready to buy these candy wrappers even at x10. Developers get rich too, because a significant part of the circulation of any coin is in the hands of the team itself. All this banquet is paid by beginners from their pocket.
Thus, the growth of Bitcoin necessarily leads to altos. The more hype accelerates, the more likely the onset of the alt season. When the Bitcoin cycle comes to an end and the price starts to fall, most newcomers leave the market, and traffic drops on exchanges. It is more unprofitable for exchanges to arrange mass pumps, as stupid buyers has become much less. The altos go into a phase of prolonged decline, where they will be accumulated for a long time by the whales or the exchanges themselves, in order to prepare for a new Bitcoin growth and alt season in a few years.