Unless you have a specific need there is no reason. So long as the domain resolves then you’re probably good. I use AWS so I can easily update the IP since I have a dynamic IP address. Some may use Cloudflare because it’s necessary to use other services or because there’s a ‘free’ option or something? I’m really not sure - I’m not familiar with Cloudflare but I see lots of people using their low-end free services for things.