(Real question, not meant to be sarcastic or challenging!) -- What are the challenges in trying to use just the ~10 core services you want/need and ignoring the others? What problems do the others you don't use cause with this use case?
A lot of newer stuff that actually scales (so Lightsail doesn't count) is entangled with "security", "observability" and "network" services. So if you just want to run EC2 + RDS today, you also have to deal with VPC, Subnets, IAM, KMS, CloudWatch, CloudTrail, etc.
Since security and logs are not optional, you have very limited choice.
Having that many required additional services means lots of hidden charges, complexity and problems. And you need a team if you're not doing small-scale stuff.
Not sure what Amazon plans to do when the m6 hardware starts wearing out.