Can anyone tell me why all coins have almost the same price trends even though they have very different algos.

BTC is the initiator it seems. When it rise, every other crypto coin rises. Very predictable.

So if BTC becomes $500k as predicted by some, can I say EOS or Eth and all other coin will increase in value exponentially too?

Or am I are lead to believe the fluctuation is independent. The price graph trends says otherwise.

Go to sites like Coingecko and see the graph trends in one page. Looks more or less similar.