Companies that depend on FOSS would contribute if the license did not explicitly tell them that they don't have to.
MPLv2/EUPL come to mind: they are compatible with proprietary products, but they make it mandatory to distribute changes/extensions of the library, not the whole product.
FOSS authors have a responsibility when they choose a permissive license.
> No they won't. They'll only contribute if they're required to
Did you actually read my comment before you answered? Because I said that copyleft licenses "make it mandatory to distribute changes/extensions", which means that companies are required to contribute if the license is reciprocal.
> At any rate, no FOSS license (that I'm aware of, or is in wide use) requires users to contribute. At most, they require that changes be made available.
Making changes available is a form of contribution. If you work on a proof of concept for a month and at the end your company decides not to use it in a product (thanks to the learning from your work), do you say that you did not contribute, so you should not be paid?
Feels like you're being pedantic just for the sake of the argument.
> Companies that depend on FOSS would contribute if the license did not explicitly tell them that they don't have to.
No they won't. They'll only contribute if they're required to, or if doing so will be beneficial to them, and they'll do that regardless of whether the license says they have to or not.
When I've worked at companies that use FOSS, and have needed to modify those sources, I'll contribute back (regardless of license) if I think that change is likely to be accepted upstream, because I'd rather not have to maintain a fork. This would fall under "contribute if doing so will be beneficial to them".
At any rate, no FOSS license (that I'm aware of, or is in wide use) requires users to contribute. At most, they require that changes be made available. There's nothing that says the changes need to be submitted (or accepted) upstream. Often getting a change into a state where it would be accepted upstream is a significant amount of work beyond what the company has already done for their own purposes, so they don't bother.