I'd disagree on politics making the space shuttle more expensive - the shuttle would have cost about the same no matter where the factories went to built it - it was a deeply flawed concept from the start, and one borne largely out of politics.
SpaceX is for the time being more or less a unicorn because it is privately held and for the time being Elon Musk does not have to answer on every decision to shareholders when it will come to that the overall level of innovation will slow down, commercial space flight isn't a bad idea but commercial altruistic space exploration is a pipe dream in the long run. You will not find many companies that will be willing to take on a 20-30 years Mars project for nothing than their own fame, yes working for NASA on such projects is very lucrative but in the absence of NASA it just wont work because there will be very little financial drive to do so. ULA/LM doesn't want to go to Mars they want NASA to choose Orion and their launcher to go to Mars and pay them heavily to develop and build it even if it never gets used.
I actually deal with this all the time in hobby electronics you buy various parts which all of them have a spec with +- certain percent and you when you buy them from a single batch you can be quite out of luck and find out that when you add them all together the tolerances just stack against your initial design.
If 0.01% is out of spec then you need tighter tolerance specs on your individual components or otherwise your design does not mathematically make sense.
This sounds like a design and process control issue as much as anything.
Not to mention that increased tolerances means higher costs and there's a point where you can't adhere to them physically and as far as real world manufacturing goes the tighter your tolerances are the tighter the control and QA needs to be which results only in diminishing returns.
When you end up manufacturing things tolerances can be skewed by a 100 different reasons from a slightly different zero and certification process to different CAD/CNC software which rounds up thing slightly differently. The ISS development actually learned quite a few things with that and they've both adjusted their process segmented the manufacturing by entire modules rather than individual parts then the only thing you need to really worry about are the tolerances for the actual dock which have quite a bit of wiggle room. If you had to make the frame for the cupola in Italy, the outer housing in France the Windows in Germany, the Shutters in the Netherlands and assemble them in the UK you would ended up with similar problems.
Saying there's nothing wrong with X you just need a better process can be said for pretty much everything but that argument rarely holds water when you deal with real world applications, there's a reason why there are entire engineering disciplines for manufacturing and process control.
So no as an Engineer you need to design tolerances not for the worse case scenario but for the actual manufacturing process you are using and the controls you can enact on that process. When that process is then spread out across as many parties as possible it's no longer the process you've started with and quite likely isn't neither and ideal process nor one you could ever really optimize.
There's a good reason why some of the worlds most advanced engineering parts are still quite often hand fitted at the end, and that's when you work with a single manufacturing process in a single factory. When you spread that out you end up with parts that sometimes can't even be hand fitted anymore.
And the reason it was a deeply flawed concept was...politics. The Shuttle that the politicians would allow NASA to build was not the Shuttle that the NASA engineers originally wanted to build.