If the system happened to break in a way that was opportune for the employer but ripped off the employee, it's better to point fingers at Oracle than your own company.
So limiting liability.
Limiting the cases of conflict of interests.
Doesn't the company face the same risk with its clients?
The risk is the appearance that the company was deliberately ripping off employees. When the employer has created their own labor tracking software, it's easier for mistakes to look deliberate.
It's easier to convince others that it was a genuine mistake when you didn't personally profit from the mistake
Corporate liability to customers and corporate liability to employees are two very different things.
Maybe not a legal reason per se, but even if you have production data access appropriately locked down there will be some people who hold the keys to the kingdom. There's a lot more risk of people peeking at things they aren't supposed to when the data in question is about their own company, friends, coworkers.