Accessibility is only not a concern for internal custom tools if you're certain you're not going to hire anybody with a disability that requires those accessibility features. (You shouldn't be certain of this, because it means you're probably breaking the law.)
Accessibility is one (important) consideration but it's true that tools with a small, known subset of users can afford to ignore some constraints. For example, if you're a small American company, your internal tools might not need to support right-to-left languages.
I don't see any reason you couldn't hire a blind level designer, but sure, there may be some subset of "internal tools" that you can make that assumption for. But the topic wasn't "internal tools for visual artists", and a lot of workplaces have internal tools that are inappropriately and unjustifiably inaccessible.
