[gabbo]

  There's no real need to be running your cache in-process with your GC'd implementation language.

Fundamentally there's no need, but in-memory caching may still be the right choice. As always, there are tradeoffs. Standing up a separate cache component incurs non-trivial costs. Your service now has a new "unit of management" - a new thing you need to deploy, monitor, and scale. It's a separate thing which might go down unless it's provisioned for sufficient load, and you need to be careful about unwittingly introducing a new bottleneck or failure mode in your system. These are all solvable problems, but solving them comes at a cost.

You can totally argue that engineers should be forced to think about and address these issues up front with more rigor, and in a perfect world I think I'd agree. :)