If you have a bug in how a lambda function is run on AWS, do you find yourself looking for the bug in firecracker? It is open source, so you technically could, but I just don't see many customers doing that. Same can be said about KNative on GCP.
Their choice in foundation OS (for lack of a better term) really should not matter to any customer.
Ok but then that is purely additive then, right? Like, "have to find someone with Illumos expertise to fix something that was never intended to be customer-facing" may not be easy, but is still easier than the impossibility of doing the same thing on AWS / Azure / Google Cloud.
Their choice in foundation OS (for lack of a better term) really should not matter to any customer.