AWS is overwhelming for most of Developers. Also vercel is focusing on ease of deployment for front end, it is also zero config, you can just deploy nextjs, react, svelte, remix apps in matter of minutes. Which is impossible with AWS
Now it's not fully baked yet. DNS configuration is broken if you want to use your own domain (see https://github.com/aws/apprunner-roadmap/issues/37 and https://github.com/aws/apprunner-roadmap/issues/65 ) but you can get around that by putting cloudFront in front with just a few more clicks (and you get the benefit of having some of your files cached if you want).