Thing is SVG is good for web and really good only for web. PDF is better for print and possibly general archival. But here is the central point as was laid upon me by a web designer recently. This guy does not do much print or SVG stuff, only about 3-4 times a year. He mainly uses Inkscape but isn't very tied to it. So he said something like this:
Look I haven't used much illustrator like only one demo period. But honestly illustrator is seemed easier to use and much nicer. The only reason I dont use illustrator now is because i dont have it installed. Then he looked at the clock on the wall and said you know it would have been cheaper to hire it for a month just for this job.
So switching to illustrator is not a big deal. Personally, and I hate to admit this, but I use illustrator ONLY for the feel of the snap in the software. Technically, Inkscape is very good but it suffers form a common open source problem, Yeah you know they can code and configure stuff but can not do usability.
Second reason is that the adobe ecosystem works very well, if your inside the ecosystem. So many people would prefer to have resources in this ecosystem. Inkscape does not work out nearly as well for print as AI does.
There is nothing wrong with using Inkscape its in many ways better for more custom SVG operations. But frankly I can see why it does not make most designers very interested.