Your employer is also a huge POS for doing this, if you know people with pull in the OSS community or software community in general you could threaten to make a stink over it. This is terrible behavior on their part.
They are obligated to take ownership.
Corporations are as moral or amoral as their leadership wants. Your average small bakery better has some good standing in a community, so it better behaves reasonably.
Their job is to keep existing, hence making some profit. That can be just enough or maximal, again depending on the wishes of the owners.
The long term value of the OSS community relationship might be more valuable than just grabbing the project. The law might explicitly not entitle them to grab it.
They can try to take ownership but are not at all obliged.
In fact the psychopatic behaviour of todays megacorps is unravelling the fabric of the societies that enable their existence.