My impression from reading the code and GitHub issues is that they're not maintained by real ".NET people" who are plugged in to all the fine details and best practices of the framework and the runtime.
StackExchange.Redis is a good example of one that is independent of MS but still very high quality.
I agree with your impression that developers of the other library don't seem to be "plugged in to" the .NET ecosystem. As an independent developer (not affiliated with Oracle or Microsoft), I've been able to influence GitHub PRs that shape the ADO.NET API for .NET 6.0, just by showing up and contributing; I haven't seen anyone from the Oracle MySQL team participating. Meanwhile, they violate basic principles of the .NET Framework Design Guidelines that have been around for over a decade (https://docs.microsoft.com/en-us/dotnet/standard/design-guid...), which makes their library feel alien to a .NET programmer (regardless of the quality issues it might have).
We ripped out the Oracle MySQL library at work and put MySqlConnector in. The high quality documentation made it really easy to understand and make adjustments for the differing behaviors between the 2 libraries. Any time I've poked into the code to try to understand some fine detail of it, I've always found it very easy to quickly understand what could be going on. It's great.