It's about building the brand, United, as just one example, have done it for years. I'd expect LFC, or any other "big" club, to be paid a fee for taking part, then there are ongoing shirt and other merchandise sales to overseas fans. TV subscriptions, etc. etc.
I can see where this developed from and think the pre-season tour of decades ago was about getting the team together, bedding in new signings, bonding and so on without distractions. All very laudable and hopefully part of a well thought through plan. Today it's about ticket sales and nothing else............Rovers went to Strasbourg last weekend.......................and we've played Accy and Blackpool, alongside others. Not much brand building going on there