That's true, but these usually come with LB and a bit of redundancy. Granted, it's not crucial at the very initial stage, but it also gives the easy of deploy. My take is that not much devs are capable of standing up their infra, even clicking it up in aws, thus services like heroku or fly.io exists and do well I presume.
Load balancers and redundancy are tech-creep, IMHO. At least in the initial stages. But I think people in tech, and in general, underestimate how performant modern hardware is. They run their service of 1/2 vCPU which was carved from some modern Intel Xeon / AMD Epyc, and they are afraid that their little startup will eat all the CPU.
You can achieve redundancy by spinning two docker instances of the same container and setting Caddy reverse proxy in front of them. You don't need k8s for that.