Welcome to Microsoft Q&A! Thanks for posting the question.
Apology for your experience with the APIM services. Developer tier is meant to be used for non-production use cases and evaluations therefore they don’t offer any SLA. Different APIM SKU's run on different backend services and according they provide different features and SLA's.
I do understand your concern and I see multiple customers voted to support VNET for Basic Tier of APIM and developer portal support for consumption tier. This is still being reviewed by the product team and they will be updating the feedback thread accordingly. You can also vote up on this feedback and also provide any feedback to the APIM service. But definitely, I will also pass your feedback to our product team.
Unfortunately, there is no way to deploy the APIM Basic Tier in a VNET. But if your requirement is similar to that you want to expose the private services then you can refer to a similar discussion.