So I brought up OIM because I have some personal experience with it and similar software. It’s main selling point is that it is extremely performing and scalabale, and it is so big (and supported by such a large company) that it has ready-made integrations with most other enterprise apps (and can be extremely flexible if you have a custom apps). These are pretty attractive qualities to giant, global companies with hundreds of thousands of employees and hundreds/thousands of apps to manage.
Competitors like SailPoint are typically more user friendly, easier to implement (as long as your implementation only integrates with common apps and doesn’t require deep customization) and comes from a generally friendlier software company, but it isn’t able to keep up performance/stability wise once you start moving above 100k-ish managed users.
The performance landscape is changing slightly now that other IdM providers are taking advantage of clouds as well for better scaling, but it’s taking some time for them to rearchitect applications to fully do so.