My reason is simple.
Today: nobody uses it. It offers virtually nothing new over Bitcoin.
Bitcoin transactions per day 270 000
Litecoin transactions per day 10 000.
Tomorrow: suppose Segwit is activated which is a big IF when F2pool controls a large share of LTC hashrate and they don't lean towards Segwit that much, but ok suppose Segwit is activated and now suddenly LTC offers something new over Bitcoin.
My assumption is that this year Bitcoin will hard fork in two chains, Core controled Segwit chain and BU chain. Community support is about equal for both in my estimates.
Bitcoin transactions volume will be divided between the two chains, 270 000 / 2 = 135 000 on each chain.
We will have coins on Bitcoin Core which can do the same as Litecoin Segwit but with 135 000 > 10 000 transaction volume and a much wider community. Litecoin will be completely irrelevant because of the Bitcoin forking in two chains. It's kind of irrelevant today but after the hard fork the irrelevance will be more pronounced.
I could be 100% wrong, do not make your trading decisions based on my "analysis" LOL