If I want to, I do. If I don’t want to, I don’t. Sometimes I’ll get through the second book and decide that I’m not interested in the third. Or I’ll try out the sequel and it’s a DNF. All those are options.
It’s no different from choosing to read the first book, really.
I’ve only read two of his books and I loved them. That said, slow and sad is a distinct stylistic choice (especially these days!), so it doesn’t surprise me that they’re divisive.