Few reasons:
1) Westerns as a genre have no interest for me - I find the whole setting and themes pretty boring. This one is completely personal and I realise it's my issue, not the games. I've tried - I even got the first RDR but they just don't compel me.
2) This one is tied to the first one - open world games have to be really good for me to play them - I don't really have the time to try and get through a massive open world game, particularly ones that are fairly slow paced.
3) Too many games to play - I'm currently playing through my SNES Mini Classic so that's taking up a lot of my time.
All those together means that even though I am slightly interested - I like games that try and be a bit different, which it seems that RDR2 has tried to be - I'm probably going to pass on it. If I have nothing much to play one summer, I might get it then to fill the Summer Holidays.