If you're already "serverless" (or want to be), it's not that easy to just "add a process". Usually if you're running a process, you're maintaining one or more virtual servers, which can be a lot more operational overhead than a Lambda.
Having said that, I agree that there seems to be an inordinate amount of effort/thought going into keeping Lambdas "warm" (i.e. always running).
I think the prevalence of these hijinks indicates that AWS Lambda should consider adding a "keep running" option that ensure the particular function is always "warm", but costs a bit more.