I don't know the logic behind it hence the reason for this post.
To understand a market, you would have to understand the people behind it.
Trends in the market, whether upwards or downwards, are usually caused by the activities of investors. If the investors deem the coin worthy of value then they will acquire the coin thus decreasing its supply while hiking its value even more. The lesser supply there is, the more demand the people has for a coin thus the higher value it will have. Now, as you know, people are usually attracted to what is currently trending and do not like the feeling of being left out. They will soon experience FOMO or fear of missing out.
Once FOMO hits, they start buying coins.
Now once bitcoin gets most of its investors holding in their coins, decreasing the supply and increasing the price, some investors might try and risk buying altcoins. Why? Because they are hoping to achieve the same performance bitcoin has. Seeing as bitcoin is the standard cryptocurrency, everything related to it would be perceived as something connected to the entire market. It is the sentiment that if bitcoin is doing well then the other altcoins might be doing as good or even better.
Of course it is all theory and a coin’s performance is still down to the individual coin.
