I'm sure the US would never think of doing something like this
The US is not the world's largest producer of semiconductors or communications equipment, China is. That's why these motherboards were all produced in China. That's why your iPhone or Android phone is produced in China. So while the US can "think" about this, they lack the means of execution, whilst China had it dropped directly in their lap.
You have no idea what you are talking about. Most of the R&D on these stuffs are in the US, and during manufacturing engineers are sent from the US to supervise the people oversea to assembly them (yes, assembly, not design).
If someone send you a different design than your original and you didn't catch it, you are dumb and should have been fired, not for security reason.
Super Micro makes good stuff, they are basically white box Dell EMC / HP Enterprise / IBM stuff at a fraction of the cost. You can remote into them for access like iKVM that your consumer grade stuff cannot, that's why you only need 10 people on premise to run a $10B data center, only to swap out bad parts, not typing on keyboards or looking at the monitors.