It's all about "catching the big fish" and "riding the waves".
As soon as a coin is released its fresh out of the box. Miners mine and hoard them for a shorter period of time until the coin gets listed on an exchange. Then they place sell orders that are way above their overall profit margin.
or do people just constantly mine the less profitable coin and try to trade the volatility of it hoping to catch a swing?
Miners already leave the scene when a certain coin becomes less profitable.