I think Azure also has more regions than AWS, but yet a smaller overall capacity probably, so it's gotta be harder to keep space capacity. It's notable the shortages are isolated to specific regions. They were possibly small to start and so it probably didn't take as much to hit capacity there? Just a guess.
That's my hunch also... Speaking for someone interested in IaaS/VDI, not all instances are available in all regions. For example, instances with GPUs are available only in North and West Europe. If you need them, and they are out of stock, you have no value of any UK or France region.
