in my opinion there is no logical answer to this question and it is not just ETH and LTC. as far as i can tell every altcoin is following bitcoin and it is actually mostly visible during the drops not the rises.
for example when bitcoin went from $8000 to $20,000 in a month last year, altcoins went up but only a little bit.
but when bitcoin fell drop $20,000 down to $8000 altcoins dropped harder, each losing 60%-80% of their value.
Yes. The three cryptocurrencies are not interconnected to each other. Though there are times that the cryptocurrencies are simultaneously goes down and rise up, the price of individual is different from others. I think that the reason why it seems like they are performing identical is because the LTC, BTC and ETH are in the top list of CMC and that's why sometimes when the demand for cryptocurrency is high, the three of it will the first bought in the market. for example when bitcoin went from $8000 to $20,000 in a month last year, altcoins went up but only a little bit.
but when bitcoin fell drop $20,000 down to $8000 altcoins dropped harder, each losing 60%-80% of their value.
