https://www.pcgamer.com/rockstar-explains-why-red-dead-redemption-2-has-a-single-protagonist/

Don’t go Googling it—Red Dead Redemption 2 still doesn’t have a PC release date, or even an announcement, but that doesn’t mean we can’t soak up every little detail in preparation for the day it inevitably happens. After all, you don’t want to be the only one who doesn’t know about Arthur Morgan, the Van der Linde gang or how you can flirt with horses. To keep us clued up, Rockstar’s revealed more about the setting, gang and why you’ll only be able to play as a single character. 

Amid its many tricks, Grand Theft Auto 5 also divided its narrative into three interweaving threads with a trio of distinct characters. You could finish up a car chase as Franklin and then switch to Trevor, who you might find sleeping off a rough night, on a bridge, without his clothes. It was great, but Rockstar set a different goal for Red Dead Redemption 2’s story.