If a project benefits you, it's worth supporting, whether or not large companies are doing so. If anything I'd flip the argument round: your support is most needed when large companies don't pull their weight. OpenJDK and the Linux kernel don't need your donation.

Also, there are plenty of good FOSS projects that aren't seeing much corporate use, such as perhaps KDE.

(Although Google are known for using Linux as a desktop OS, perhaps including KDE, I'm not certain.)