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.