And many proprietary pieces of software license components from other proprietary pieces of software, so that even if they did want to open their code they'd have to strip pieces out of it anyway which doesn't really help the cause of distros integrating it. And even if it did, then the developers are reliant on the maintainers for their relationship to their customers. Have an issue with the product? Oh, it turns out that's because of this patch made by the maintainer of the package for that distro, who now has to be contacted and convinced to fix it, which they may decide not to for arbitrary reasons. Even open source developers have problems with this!
If you need to strip out some parts and there is enough will in the community to replace those pieces that you stripped out, then it will happen. If you have a product that is anywhere near being popular among the FOSS developer communities then I don't think it makes sense for you to claim that this will doesn't exist, or that distro maintainers will lose interest.