Why is it the US has never adopted the metric system yet build products using metric bolts..
Adoption is a matter of practice. Anyone who has a 10 mm nut driver for our vehicle batteries has in fact adopted it. But we remain an unfortunate mix.
Ironically, our engineering studies have been in purely metric for a very long time!
The new tools and dies that created your snowblower were manufactured in metric but no one is going to throw existing manufacturing equipment (there is some left) and tools and dies in the garbage just because of this reason, and rightfully so. For repairing US goods including old vehicles, tool makers must still sell Imperial tools. Thus Imperial knowledge cannot go away completely. The US was a huge manufacturer for a long time and thus by pure volume, Imperial system attrition will be slow for us.
In contrast to that the US federal government is in charge of all major standards in some form. If they ignore an idea it will not happen. If they have any sort of initiative then POOF! it will happen like magic. The last major metric-related incident on a federal level (that I know of) was a petition for metric conversion to the White House in 2012. The Federal advisor responded to the petition that metric/Imperial is a choice for individuals. Think of a White House that sees fit to issue a mandate that individuals must get a vaccine but which called the measuring system so unimportant that we should still choose as individuals.
So the federal government has detached itself from the issue they claim? The National Weather Service goes back to the 1800's and is a veritable part of our federal government. Temperature measurement is significant in weather and science but our country still reports in Fahrenheit. There are infinite regulations and fees, including for "global warming" originating at the Environmental Protection Agency, another federal agency. They significantly affect the cost and complexity of manufacturing and the making of vehicles. But these bodies do not see fit to push for reporting temperature like the entire rest of the world does?
Our General Accounting Office performed studies indicating that a change to metric would cost too much. Since we print money on demand, the idea of excessive cost is outright vapid. Look where the money goes to. That is the issue.
Not just twenty-two years ago NASA lost a Mars orbiter due to Imperial/metric translation issues. We only have brief respites of this idiocy since then. NASA's new effort to replicate our last manned moon mission appeared
extremely promising two years ago. But in an instant it appears that it may actually die on the vine due to defunding. Our leaders are actually repeating 1966 and 2010 (the cancellation of, at the time the most recent rocket replacement program) for the umpteenth time, taking cash from the very precipice of the human endeavor and allocating it to social wealth redistribution.
Why not switch to metric?
Because science, the human endeavor, math, and metric unification are distinctly not a priority for the majority who have shaped our government and country for the last 100 years. The federal budget allocations and the leading ideas coming out of the mouths of our leaders on television right now distinctly reflect this vile fact.