What I think is really unfair to mention is that unDraw has contributed to the commoditization of illustrations. On the contrary, there have been many many projects available to illustrators just because the initial design/proposal/prototype could be built with that and win over the clients. Project designs that would otherwise use photographs but not illustrations.
Sites like Upwork, Freelancer, etc. existed long before unDraw and you could find creative work there for truly humiliating prices. It's extremely inaccurate to blame unDraw for that.
The fact is that unDraw helped bring attention to illustrators and illustrations, which were called icons even a few years ago, by opening up a discussion and many new projects.
I'm willing to throw a few bucks at that. For clip art (SVG) in a blog post, I'll throw $10-$15 at that. Per post. But the art needs to speak to me or otherwise just "click" with my yet-to-be-defined vision for the content. I don't know what will click until I see it. I also don't want to waste either party's time with my hemming and hawing, trying to put a feeling into words so I can describe to the designer... how I think they should do their job. I'm not the expert. I just fail at communicating. It's much easier on everyone if I see it already done or otherwise 95% of the way there.
Sites like these help me a lot more with finding things that just "click." At least a lot more than the alternatives of finding someone on Upwork, et al.