I love and highly value open-source software. I try to donate to the creators of every piece of it I use, and make a rule of it if I intend to use it commercially. I admire open-source developers and hope for all of them to make a great living doing what they do, regardless of whether they themselves want that.

That said, yes, I think it's undeniable that offering one's work for free decreases its value in the market. Is that inherently bad? Certainly not, but it does make it harder to make a living doing it. Devs are doing okay right now because of how things are going—illustrators, not so much.

Projects like this rub me the wrong way for two reasons:

1. I've personally lost several contracts to people who charged very little or nothing for the (oftentimes very good) work they do for well-funded, plenty-capable-of-paying-fair-wages companies. I fully recognize this is just sour grapes, but hey, I'm eatin' 'em. Wouldn't you be frustrated to lose work to someone offering to do it for free for a client who intended to get rich using it?

2. Illustrations like these are, these days, intrinsically commercial and aimed at customer acquisition for businesses. These are for marketing; for raking in money. They aren't being presented as (though I concede they could be used as) jumping off points for artistic exploration or further creative development. I recognize others may not agree with me here, but that makes them somewhat antithetical to the open-source … cause? attitude? whatever.

A possible third, but more loosey-goosey point is that because the effectiveness and quality of illustration is much more subjective and difficult to measure than software:

Reasonably efficient functionality seems to be a satisfactory baseline for most people evaluating software, so that gives them a way to make a rudimentary cost analysis on it. A free, open-source search tool is great if what you need is a search tool, but if you need a membership management system, you can't just throw the free search tool on your site and call it good.

With illustration, however, 'screen that vaguely resembles a dashboard', or 'people in a meeting', or 'someone walking through a park' can all theoretically be used to visually communicate countless different service offerings or brand principles (which is precisely what makes these libraries so popular and effective), especially if you don't have a tuned or critical eye, or simply don't have much incentive to care about being more precise. It's therefor much more possible and more likely that a company can go years making tons of money without ever paying a penny for illustrations, despite those illustrations potentially being of great value to them. Which, yeah, bravo for them, I guess? But that sucks for illustrators.