My guess is the biggest reason is to be closer to friends, family, and/or community. Having help to raise kids is huge. And when you have kids, you begin to focus on the real important things in life, and the type of environment you want your children to grow up in, and speaking for myself personally, I wanted them around as much family and love as possible.
It's also easier to do this now with more remote work opportunities and with more tech hubs across the country now.
Yeah, one of my wife and I's biggest mistakes was staying here in Ontario and settling even deeper into our property after her mother passed away. We should have moved at least temporarily to Alberta where my parents are, because it's been so hard raising kids (and now teens) without any close support. And now we're kind of stuck here, so. When you have kids, having close and extended family nearby is worth more than anything.
It's also easier to do this now with more remote work opportunities and with more tech hubs across the country now.