Why did Jesus include wife in the list of things you can leave and still be blessed (Luke 18:28-30) if elsewhere Jesus commands against divorce, and Paul says that one should not leave one's spouse (even if they are an unbeliever) if the spouse is willing to stay?
Very interesting question. One could ask the same question about the rest of it, as well: why would I leave my kids, or parents, or anyone "for the kingdom of God"? I think it makes sense that he is referring to possible consequences of taking a stand for the faith (persecution, being forcibly parted from our spouse, etc). Also take a look at Matthew 10:34-39.