The root problem is that AWS charges way too much for data egress, and then sell cheap instances bundled with several times their purchase worth of egress.
AWS doesn't want people putting their apps behind LightSail instances solely for the purpose of reducing data egress costs. I think it's a very reasonable rule considering the situation they put themselves in.
The problem of course is it quickly leads to bad faith instances of people doing just that, then claiming not to be doing it. But it's going to be impossible for them to write a lawyer-proof rule that prevents it while also not preventing legitimate usage.
Like, if I run a web app that accepts requests to example.com/mybucket/myfile.zip, and the app merely pulls myfile.zip from the mybucket S3 bucket and sends it, then yeah, that's a pretty cut-and-dry case of using LightSail to avoid egress fees from S3.
But what if I'm using a LightSail instance as just a load balancer in front of EC2, because I don't think an ELB/ALB is flexible enough? That starts to be a bit more of a grey area.
