Litecoin has been around for 10 years, so it's an old and reputable cryptocurrency which people closely associate with Bitcoin. It's not a rival of Bitcoin, it's just a friendly modification that was by Bitcoin's side for all these years. So I think that Litecoin will always be a popular choice for those who support Bitcoin but are open to trying something else if it helps with the fees, for instance. Bitcoin Cash, on the other hand, is clearly a rival of Bitcoin, and its creation threatened Bitcoin from the very beginning, putting its integrity at risk and splitting the community into believers and non-believers. So people who support Bitcoin aren't very likely to turn to Bitcoin Cash, while they can be quite open to Litecoin.