Again, stop thinking rationally - this isn't about revenue, it's corporate theater.
They're clutching at legal action because it looks decisive to non-gaming investors who don't understand the ecosystem. Going after "IP infringement" sounds like protecting valuable assets, when it's really just expensive procrastination.
Any pivot to revenue-sharing or cooperation would require admitting incompetence and failure, at least on some level. They cannot do that - not at any cost, as it would paint a target on them.
I've seen this before in failing publishers. If you know how they operate - this isn't the least bit surprising.