It isn't the way of modern football, it is the way of society and it always has been. People want to attatch themselves to success and feel like they are a part of it, the tribal nature of football means that
generall when a club is successful at a certain point then people of a certain age become supporters of that club for the rest of their lives, most of the time passing it on to their children.
Every club since about the 50's and probably before that has been the most successful of their time has brought in supporters from all over the world, which brings in money, which allows those teams to cement their position at the top of the tree barring a catastrophe.
Yes it is great when you have local supporters who identify with a club, this happens with every club, especially the big clubs but it is also great to have people not from the city want to be associated with that club and therefore bring in the revenue to allow the club to actually be a success.
Tbph, even in Liverpool the split probably isn't 50/50, judging from personal experience only there seems to be a lot more Liverpool fans than Everton fans about
but that isn't a petty argument I want to get in to as it is purely anecdotal.
Edit: And there are a significant amount of Norweigan supporters of Liverpool who have season tickets and fly over for every single game. They are from out of town
but manage to ingratiate themselves within the culture of the club.