The Developer would have to divert a significant amount of time to re-work to comply with Apple's current standards. The work involved might require a complete rebuild of the game --- one can imagine how that is not an enticing project.
That is unlikely to happen as the Developer is busy with working on his next project,
Archaelund. That game will be a PC only game to avoid the numerous issues with smart phone devices, which include compatibility and size restraints.
For fairness, Apple has traditionally defended it's policies as necessary for security and functionality of Apple services. There is some truth to that --- the more flexible a platform the more room for vulnerabilities and compatibilities issues to pop-up.
As a personal comment, I believe it's a case of Apple using legit security concerns to to justify anti-competitive business policies that go well beyond what is actually required to address security issues.
This lengthy comment is aimed towards highlighting why the iOS update isn't a simple matter to resolve. Some players are a bit frustrated and don't understand the complex reality of working with Apple.