I'm not completely sure because I'm not familiar with the topic, but maybe it has to do with the fact that even when they sue you with an impossible-to-win lawsuit, they can destroy you with the cash you need to expend to even start defending yourself.
This can also destroy investment rounds for many startups.
Okay but they can do that even if you don't use Java.
And even if you don't do any bussiness with them.
Oracle can sue anyone, they sue a lot.
Like most companies they only do so if they think they can make a profit.
They could sue you, with a higher chance of winning, for using a python, a js or a ruby than for using OpenJDK derived code.