[SethMLarson]

Because every CI/ID provider has a different set of claims and behaviors that would constitute a "secure" policy for verification. If there was one singular way to do that then we could, but there isn't yet so PyPI needs to onboard providers piecemeal. The work to add a new provider is not massive, the reason there are not tons of providers isn't because the work is hard but rather because people are voting with their feet so Github and Gitlab make sense as initial providers to support.