The big problem here is that it sounds like you took an "if I build it they will come" approach, which is just never viable for this type of thing.

The reality is that because no one is using this protocol, your pitch is a really bad one for anyone you're pitching to - you think they should spend the time and effort to use your protocol, and what will they get for their effort? Nothing. No one else is using it, so they'll be implementing an interoperability protocol that doesn't actually make them interoperable with anyone else. Why would anyone ever do that? Why wouldn't they wait and see if others adopt it first?

This whole post honestly feels very self-centered - particularly "re-explain how common-data-model helps us (why are we explaing this to CTOs and techinical founders?)". You have to explain it because you're asking them to do work. They get to ask you whatever they want, as many times as they want, because you're not presently offering any value whatsoever. You need to stop assuming that everyone else shares beliefs about your protocol that are obvious to you, the person who spent a lot of time and effort planning and building it.

Instead, put yourself in their shoes - what would make this attractive to them? Since we're talking about interoperability, clearly if there were a lot of other folks using it, that would be a selling point. You obviously can't offer that, but you could try to get soft commitments that companies would use it if a critical mass of other companies did too - if you get enough of those commitments, you can then show that there's potential value.

You really need to find someone who understands sales or business development to guide you here. It sounds like you built this with no real input from anyone, and now you're taking it to companies, explaining what it does and getting frustrated that they aren't responding positively.

The one thing that it doesn't seem that you're doing at all in those meetings is asking questions. Why are you on HN asking what you're missing and what it would take to get people to sue your protocol?

Ask the people who you want to use it! When you're in those meetings, you should be asking people what would make this attractive to them and what would incentivize them to implement it. What you're doing right now is selling, and the way that you sell someone something is by understanding what problems they're facing and providing them a solution to those problems. The first step in that is asking questions - otherwise you're the car salesman trying to sell a guy a sports car because you think sports cars are neat, and you never bothered to find out that he's looking for something to take his five kids to their sports practices.

If you're serious about making this work, I really recommend finding someone with business development experience to help you out - if you don't, you're just going to keep spinning your wheels until the folks you're trying to convince just don't want to spend more time dealing with you. I know folks on HN are often deeply scornful of BD, but this is exactly what it's about - understanding the needs of the folks you want to work with and brokering deals that are attractive to them.