I wonder how people are using them in a way that is not distracting to the main content. I've found that high-frequency patterns (small details with sharp transitions) can be a bit distracting, but I haven't found a good solution that doesn't compromise the beauty of the backgrounds.
Edit: upon further investigation, access isn't something that's just thrown around willy nilly! It usually goes for $120/yr!
The SVG code is well written. It is neither Adobe bloat-spam-slop and neither is it overly SVGOMG'd.
For picky SVG people you could have some easy way to present the code. Only a minority value quality SVG, artworkers do not look at SVG code and coders just see SVG as 'assets' from the artworker. SVG therefore has not evolved to a full art form.
Summary: You can use graphics in personal or commercial projects, you cannot use the graphics as the primary integrity of your product, you must provide attribution (svgbackgrounds.com/attribution)
And before anyone rips off my head, attribution can be placed inside commented out code, so it doesn't need to take away from your design.