Isn't the typical licensing model for open-source projects designed to differentiate between personal and commercial usage? Or is the real challenge that enforcing such licensing terms is practically unfeasible?

We use the Boost license which does not distinguish personal from commercial use. This is on purpose. We have no agenda for anyone's use of D. We are especially happy to hear from users who have made a lot of money from using D.

Open source business models differentiate by providing value to commercial entities (support, extended features, whatever.)

Traditional open source licenses and definitions of open source demand that the licenses not differentiate between different use types (personal, commercial, governmental, etc.) Newer licenses are coming up that do differentiate. Traditional open source orgs are often saying that they're source available, not open source.

No, they are not. And the most popular licenses (Apache-style) these days don't even require commercial entities that fork your project to contribute back their changes. Free software / copyleft licenses like the GPL which do require that are these days shunned by many.

"Open source" has become synonymous with "free labour" for a lot of firms, and there's a whole class of SaaS projects which amount to gluing together other people's open source work and then supporting it.

I think this was all fine for people during boom time; you built your resume up on GitHub, you got street cred, often your employer paid for you to work on it. But I think it's starting to lose its sheen for some people.

Here at the D Language Foundation, we don't shame people into contributing. We point out how it is worth their while to donate.

I’ll use this opportunity to say that D Lang is awesome and that I wish it gains wider adoption. I simply love that language and the community and I thank you for everything you do.

On topic, indeed, shaming is never an option. But still I wish companies would donate to projects - in some countries there are even tax incentives to do so, and the benefit is that they essentially externalise development of a valuable tool for them. Also would earn a lot of good will - as steam does (while not sponsoring money directly).

It's the kind words from people like you that give us rocket fuel!