I agree, ideally they'd be more transparent. But I think the reason they do this with their investments, not just in Pakistan but all BRI projects, is partly to avoid exposure of their own companies and state-institutions to foreign scrutiny and public record. It's not really to do with us, a good example of this is that they of course shared the details with the government of Pakistan and all stakeholders here, but they deeply objected to sharing any info with Pakistan's multilateral western lenders of last resort like the IMF. They don't want prying eyes from other nations on their affairs, nor do they want the financial records of their BRI companies exposed to scrutiny by third-party foreign powers. You see CPEC for us is strategically and economically important, it's huge. Eqaully for the Chinese, this is a mega-project in which they've invested lots of money and political capital, it is the flagship project of Xi Jinping and also China's power projection internationally, it's understandable imo that they'd be protective.
Also, I believe it might be that they create bespoke deals for everyone too, financing terms and contractual agreements based on the project and nation. Meaning for example, the financing of a dam in Pakistan might have different conditions to Gwadar port, the financing terms of Hambantota port in Sri Lanka which was part financed by EXIM China might be very different to Gwadar's terms and arrangements, despite both being BRI port projects. Chinese probably want more freedom to tailor the project financing without comparisons between projects, with scrutiny also comes politicization, I think their philosophy is different the western model of transparency. This is just my own personal assessment, truth might be different.
And I fully agree with the rest of your post.
How hard is it for Western intelligence agencies to get hold of CPEC records from honest patriotic Pakistani bureaucrat ?