I feel this is answered by Free Software philosophy 101.

Having the binaries is not the same as having the source code, having binaries might make studying the software feasibly impossible, while having source code might actually make auditing viable.

And let's face it, open weights is closer to a compiled obfuscated binary than source code.

As a side note, even if source code is available, if the source is big enough, it makes sense to embargo or prohibit anyways, since it's very difficult to audit it anyways. Especially if problems are already found.