They're the cheapest EC2 instance type, so they're very attractive to small scale deployments like side projects, personal sites etc. (basically anything that can run on one or two small nodes) where budget is a major concern. The t4g.micro is in the free tier as well, so that'll help.

I host a few very low traffic sites & I'm in the process of switching from a basic DO Droplet to a pair of low-end Gravitons. Will save me money and give better peak performance for my workloads.