...I think that some time the automakers are at fault...
...It took 2 years to have my air bags replaced.
...the parts are not available at this present time...
...My wife's ML350 is still waiting for its airbag...
And the ugly truth-reality comes out. First, parts used in manufacture (on the assembly line) always take precedence over service or recall parts. NHTSA or no NHTSA, recall or not, no automaker is going to stop production because of parts needs elsewhere in "the system". This brings to mind the other truth: service parts are handled and even purchased completely separately from parts used for assembly. This is why to many it is mind boggling why (extreme example here) Ford will manufacture 2,300 F-series trucks a day, but will often have a shortage of parts for recall work or service work. The normal person's mind can't fathom this. While that's an extreme example the same thing holds true for other manufacturers.
With some of these recent recalls--such as FCA's announcement the other day
http://money.cnn.com/2018/05/25/autos/fca-recall-cruise-control/index.html that involved 4.8 million cars, once they determine the fix, then obtaining parts (or even a software patch) and deploying it worldwide, and then getting those 4.8 million vehicles in is a gargantuan task. 4.8 million of anything is trouble unto itself.
The darling of the tech world, Elon Musk and Tesla, is learning the hard way that manufacturing cars isn't easy.