It's also tooling. Professional grade PCB design software can be acquired for a few kilobucks per year and OSS versions (KiCAD) are pretty useable. Professional grade IC design software is hundreds of thousands per year and open source competitors are barely usable in comparison. I do share your hopes though, democratizing IC design even a little would be a huge boon to hardware development.
You can route DDR in KiCad and there are some online reports of people doing that. KiCad is not as nice as the paid software and there are shortcomings but I think 'pretty useable' covers its status accurately.
I think that's hyperbolic. There are several designs advertised as being designed in KiCAD that have DDR which means there are way more not being advertised.
