Which is how it should be, IMO - the base model is available to anyone for free. If you want extra features after using the base model, then a small donation to the developers for their time is a worthwhile tradeoff.
Then you're stuck: the community member could certainly fork the project with their new feature, or maintain a patchset and forward-port to each new version of the original software, but both of those things are a ton of work.
Meanwhile, users are the ones who lose out; someone decided to build the feature and give it away for free, but users have to jump through hoops to use it.
As someone who has done a lot of open source work over the past ~20 years, I don't think anyone is entitled to find a business model in there. Sure, if you can find a way to work on your project full time but still support yourself, that's great. But often the ways people do so make for some (IMO) bad trade offs and perverse incentives.
I like the dual-licensing approach, where commercial users need to pay, but that's not workable for all projects.
See VirtualBox, and to some extent Chrome. For VirtualBox, I'm sure that the Extension Pack could be covered with an open-source effort by the community, and in the case of Chrome, their refusal to accept *BSD patches.
Accepting 'portability patch' isn't free..
It doesnt benefit from the massive scale revenue, but if it's paid for your time...