We need to remember that these companies started offering hosting services to monetise their latent capacity. It's therefore easy to set up and designed in a way that costs 'eye-watering' amounts of money if you take huge volumes of resource that requires them to add more capacity.
Hyperscale is super easy and has the ability to do pretty much anything you want it to, which is great if you're building something complex like an AI application. There's no infrastructure capex or capacity planning. It's the perfect dev environment. The issues normally start when you use the hyperscale dev environment for production. Resource intensive applications like AI create so much cost it can cripple the growth of the start-up.
For production environments, a specialist hosting provider can offer environments that perform much better and cost considerably less. Bare metal and VMs in a private cluster, won't be as slick and instant as through a hyperscaler, but the performance and cost advantages make it by far the better way of doing things.