Problem is they are all built up of many smaller pieces as well - you may need the information about them at different points. For ex. EC2 drives are from EBS. if you need a load balancer ELB. You probably use S3 for some or other reason (log exports etc at least). You want a db - RDS makes it easier. Dynamo is literally a button click away. Kubernetes? Well there is EKS.
Yes you can probably launch your own cache fleet using a bunch of ec2 boxes - but you don't get all the low level hooks Elasticache gets. You don't get the pricing discounts either (I remember cross zone replication or something being distinctly free for ec2 but you pay for network. Same with dynamo - access from all zones cost the same pretty much IIRC).
If you are going to make the dive, it is worth spending the time. I would do a small overview bootcamp somewhere so that you know what's available and then start digging in for each new service you take up.
I look at the whole stack and aside from IAM and EC2, and ECS I think you could get by without a lot of those products.