I'd guess it's more to scoop up mindshare and make getting started easier, which almost assuredly leads to future upsells. That developer who starts prototyping a project on AWS instead of DigitalOcean now might make them $$$$ they otherwise wouldn't have down the line when that person needs to scale and doesn't want the huge pain of switching providers.
I don't disagree with your details, but you're arguing in a circle (here and in another similar comment).
Let's assume, based on the evidence at hand, that Amazon is rolling out Amazon Lightsail, and that as such, they're willing to do work (create business plans and write software) to court the $5/month market. In that case, it's a relevant comment for people to write "I can afford $5/month, or even $20, but I can't afford unlimited liability, even with what I know about AWS customer service, so I cannot use this product." It's relevant because it suggests that there's anxiety that is preventing uptake, which can be solved by a combination of writing software and internally committing themselves to eat the loss if the software is imperfect (as others have said, stopping service actually-on-time is actually harder than it sounds, but the provider can always just eat the loss, invisibly to the seller).
Your (probably-correct) observation that Amazon doesn't really care about the penny-ante user's money (in the short term) is beside the point.
