I stumbled upon this post and I'm a bit confused because what you are saying appears to be different than what the GitHub repository license file says.
In this post, and on this page: http://esotericsoftware.com/spine-runtimes
"The official runtimes are available on GitHub and licensing Spine grants permission to use the runtimes in your applications. All of the source code is provided, which is essential for such a fundamental component of your games." Pretty simple. You can use it in your apps.
But on the GitHub license file it says: https://github.com/EsotericSoftware/spine-runtimes/tree/3.6/spine-c
You are granted a perpetual, non-exclusive, non-sublicensable, and non-transferable license to use, install, execute, and perform the Spine Runtimes software and derivative works solely for personal or internal use. Without the written permission of Esoteric Software (see Section 2 of the Spine Software License Agreement), you may not (a) modify, translate, adapt, or develop new applications using the Spine Runtimes or otherwise create derivative works or improvements of the Spine Runtimes or (b) remove, delete, alter, or obscure any trademarks or any copyright, trademark, patent, or other intellectual property or proprietary rights notices on or in the Software, including any copy thereof. Redistributions in binary or source form must include this license and terms.
Which basically means you can't do anything with it without written permission, that any and all games written with your library will mean you must also contain the license and terms.
There is no comment in this license file concerning commercial distribution at all, which generally means you can't do anything with it. This all seems quite restrictive if the goal is to create adoption of the product.
I, for one, am working on a new engine. We'd love to add native support, but don't see how that's possible without writing from scratch. I also don't see how to get it in the hands of the users and let them use it very easily with these restrictions.
Could you clarify the intent and update the licensing files if they aren't accurate?