Microsoft learned about the power of proprietary lock-in from Wordperfect.
You’re wanting proprietary software vendors to make it easier for other people to take their customer base.
This is one of those cases where what the company thinks is best for it may not be aligning well with what's best for the customer. Format lock-in means you have less need to rely on the quality of your software to keep your customers.
Notice I haven't said anything about forcing Microsoft to make Exchange more interoperable. But its lack of interoperability (plus CALs and that monstrosity of a database) are very good reasons to avoid it or leave it if possible.
I hate that jet database as much as anyone, but my job is to deal with it, just like I had to deal with their stupid free/busy architecture before they changed it. Somehow what's important to me gets re-characterized as "cupholders", and what's important to you is all that anybody should really care about.