> wouldn't China simply create their own bespoke hardware accelerators? So what's stopping them?
Fabrication.
SMEE is supposedly able to mass produce 28nm lithography machines, but most modern (2016/Pascal onwards) GPUs are fabricated using 16nm lithography or lower (eg. Ampere uses a 7nm process, and there are multiple newer architectures in the pipeline that leverage 3nm fabrication processes at Samsung, TSMC, and Intel).
Chinese companies like SMEE are trying, but it will take 3-5 years to reach 16nm lithography at scale.
Also, GPUs are being limited for simulation (aka Nuclear weapons testing) reasons - not "AI" - as just about every country except North Korea honors the Comprehensive Nuclear Test Ban Treaty, forcing countries to test using HPC (edit: also used for Jet Turbine simulation a la Autodesk Federal).
A 28nm process is more than enough to make EWS, Avionics, and Precision weapons, which is what Russia uses to manufacture the Elbus-8s chipset domestically.
This is partially related to why companies like Nvidia has begun moving fabrication to Samsung fabs over TSMC in the short term, as SK has a formal defense agreement unlike Taiwan.