I'm glad to hear you've had a good experience with v0! We have not made many (if any) changes to v0 for some time now--I would be surprised if you were suddenly having issues with v0. If I understand your question, you are asking why v1 is not backwards compatible with v0, or why migrating to v1 requires changing your code. I'm glad you asked.
For context, we released API v1 last year, which is our current major version. API v1 is a fundamentally different structure that offers a number of improvements over v0, and is not backwards compatible in most cases. One of the major goals in v1 is to organize the information more intuitively than the fairly flat structure that v0 provided. Therefore, we are releasing new features exclusively on v1 and encourage our customers to adopt v1 at their convenience to take advantage of the additional features. Granted, v0 still works and is available for legacy scripts that still use it.
So to answer your question directly: it's effectively impossible to not have breaking changes between major API release versions. In fact, avoiding breaking changes defeats the (perhaps entire) purpose of versioning the API.
We avoid breaking changes within a version number. It is rare to make a breaking change within a given version number--it would normally be a result of a bug that requires a breaking change to fix, and never just for the sake of it. In any case, adaptation and evolution is an inevitable fact of the software development lifecycle. Ideally, major API release versions (e.g. v0, v1) have the lifecycle of a piece of hardware, or longer. In practice, the lifecycle of an API version will vary based on the industry.
Have you seen our interactive documentation site? It covers all of the endpoints in detail, and is searchable. We're always looking for feedback on our documentation and how it can make our developers' lives easier--we fully understand that most folks using a network platform API will be netadmins first, and developers second. In any case, keeping current on updates to the API is similar to keeping current on a Cisco certification, where the topics, and areas of focus, change over time.
You can also post questions here about the specific things you'd like to do with the API, and there are a lot of folks here willing to help! Long term, I think you'll find that it's overall easier to get things done with v1, despite the adjustment phase.