I think you must be missing what's going on here. This removes the requirement to integrate more directly with MS Office, instead relying on a separate library that is provided standalone from Office and thus allows saving to Excel. We've had zero issues with using this library, which is actually pretty uncommon for us.
The issue is flexibility. Using third party libraries, you can integrate with Excel or with anything else. Using the Office libraries, every user, in ever system, is bound by the limitations of the most problematic. It makes deployments more costly, and more complex.
That's true, it's the kind of self perpetuating lock-in that has served Microsoft so well. People use Excel, and they ask for saving to Excel spreadsheet, so we create the integration specially to allow Excel and not include ODF, then we help keep the industry locked into using Excel because that's all we support unless you want to just save to CSV.
As for the cost and complexity of deployments... that could be true, except that the installation of our main software is already so complex and costly that dealing with potentially installing this library is the easiest part. I think we probably only have one other developer who would be able to figure out how to install it. I've never heard of any client's IT that have been able to figure out how to install it (just calls from those who have tried), client services has to do literally every install.