I just... I don't really understand why startups even use AWS, GC, or any other cloud hosted software? Hetzner, etc. Are all extremely cheap, and honestly scale so well... Code nowadays is cheaper for configs, and having full control over your compute is... liberating.
Perhaps Railway does a bit more than what you think, they have some great functionality (I'm not affiliated with them). Check out [Features | Railway](https://railway.com/features) "PR Environments", they are incredible for the QA process
Low cost to entry, easy to get scale from the beginning if you need it. The large cloud providers throw free credit at startups to lock them in all the time. I had a short lived stint trying to get my own startup off the ground and it was really easy to get free compute from Google with no strings attached. This was many years ago now, but I would be surprised if it is any different.
I am with you entirely and would not have taken that route today, but it is really easy to see why people go that route.
A few years ago, when I was kinda active in the startup scene in my area, you have people selling access to cloud credits with penny-on-the-dollar price. The credits are given out liberally to big-corps, organization by AWS/GCP, through workshops, webinars, events. All in the hope of roping the departments into building MVPs, demos on AWS/GCP, but people also find a way to cheat on that system and make some quick bucks.
I know a startup of my acquaintances that have been running on AWS for 5 years straight without paying a single dollar to AWS. When the credits almost run out, they started to migrate their data over to another account with credit. That happened twice already.
It helps to have a portable, replicable IaC config. But also this is sustainable because they are a pretty small struggling shop. You will probably not be able to do this if you are trying to maintain more than 3 nines for an enterprise client.
Oh absolutely... and many use architectures that have evolved out of the needs of really big companies and are not really a good fit for a startup. But I guess they want to be "ready for growth".