I'm not a Vercel fan, but the whole pitch of PaaS is you get more than just a provisioned server for your application. The 20$/month/dev is vercel's own concept of what that Dev Experience costs with a profit margin + average usage fees paid to AWS baked-in. They might leave that average low, but they assume you're here because you like vercel's tooling, not that you're price shopping for $/BitsTx'd. AWS will always win in that, because vercel is also AWS with some dipping mustards they really want you to lock into.
The hobby plan is a loss leader to get developers into the vercel tooling. If you go over the free tier's bandwidth limit, you've exceeded what vercel believes that developer goodwill is worth for a single account. If they allowed you to pay for extra bandwidth on your free plan, it would make vercel look like a crap cloud platform, because all you're doing at that point is paying a premium for AWS, and a kneecapped version of their developer tooling. They really want you to pay the 20$/month/dev and experience everything in vercel's platform because that's their only product. Honestly... no fault to them on that.
Maybe they'd gain some developer positivity about letting you dig your account out of the "exceeding the hobby limits" hole that's easy to fall into, but the AWS cost for them is already spent, and that was all the budget for appeasing you. You'll have to pay them to pay AWS anyway, so they draw a hard line at that point and demand you also pay to use the vercel tooling, which is the only thing they make. (or, in theory, telling you to go pay AWS yourself if the tooling is unimportant to you.)
Just to make it clear, I genuinely think they offer a crap deal. They justify being expensive, but what the end user gets in return is not worth it IMO. Do not host anything on Vercel if you can avoid it.
The point I'm making is that the billing becomes very clear once you treat them like a PaaS, not a cloud platform. It's like buying individual seats for corporate software that just happens to also host your application as a side effect. I feel like they make this fact pretty clear on the pricing page.
"$20/month" = a single license for vercel's own tooling
"+ additional usage" = whatever AWS + markup costs... they SHOULD link to the /limits docs [0] from here
"$20 of included usage credit" = "free" coupon to use the overpriced AWS services with the pitiful soft-limits listed in detail below
"Drag the sliders. Watch the $20 plan disappear." is a misreading of vercel's pricing chart. "Vercel Pro" was never 20$, especially not for 5 users, since that's 5 licenses for vercel's tooling, which is the ONLY thing they make here. You essentially get a coupon letting you use that tooling on AWS via their control panel, but beyond that they have 0 involvement in the cloud market. They list the soft limits under the column in the price chart, and they have that /limits page detailing their insanely marked up overage charges. [0] IMO, that's not hidden, it's just a bad deal.
They selfishly assume their tooling IS the product you're here for and whatever hurdles exist to use it will just be tanked. "theupsellgame.com" also complains that the hobby plan has no way to pay for it. Why would I sell the supermarket apples at my fruit stand placed directly in-front of the supermarket if you aren't going to also buy my superior Apple Eater's Experience package.
Again, I think they're leeches. I just think this site uses weak arguments for why Vercel is awful.
The hobby plan is a loss leader to get developers into the vercel tooling. If you go over the free tier's bandwidth limit, you've exceeded what vercel believes that developer goodwill is worth for a single account. If they allowed you to pay for extra bandwidth on your free plan, it would make vercel look like a crap cloud platform, because all you're doing at that point is paying a premium for AWS, and a kneecapped version of their developer tooling. They really want you to pay the 20$/month/dev and experience everything in vercel's platform because that's their only product. Honestly... no fault to them on that.
Maybe they'd gain some developer positivity about letting you dig your account out of the "exceeding the hobby limits" hole that's easy to fall into, but the AWS cost for them is already spent, and that was all the budget for appeasing you. You'll have to pay them to pay AWS anyway, so they draw a hard line at that point and demand you also pay to use the vercel tooling, which is the only thing they make. (or, in theory, telling you to go pay AWS yourself if the tooling is unimportant to you.)
They will sell you pay-as-you-go services... but only once you pay their 20$: https://vercel.com/docs/limits#on-demand-resources-for-pro
Over all, I hate it. But I don't think there's anything too hidden about it, or at least no more than any other PaaS provider.