Why does Vercel recommend using the www subdomain as the primary domain?

I’m setting up a domain with Vercel, let's say xyz.com. I want my application to be accessible from both xyz.com and www.xyz.com, with SSL coverage for both.

Vercel's recommended approach is to:

Instead of:

My question is—why? It feels like most modern websites redirect the www subdomain to the main domain rather than the other way around. What’s the reasoning behind Vercel’s recommendation?

Would love to hear insights from others who have dealt with this.