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Unless you're a vendor's largest client, or one of the largest companies in the world, I'm not sure how you "force" another company to do something. (I've always wanted to be on a call between two of the ten largest companies in the world - just to hear how they negotiate with a near peer and not be able to stonewall everything.)
It's unfortunate when companies aren't willing to use automated processes, but there are numerous (besides legal) reasons NOT to participate. Vendors have their own workflow efficiencies; we all count on those efficiencies when retaining third parties. Their methods of responding to the flood of questions they receive will have been worked out over time to be most efficient for ----themselves. That efficiency contributes to their overall value proposition for us.