We are used to 2 liter bottles, so we still use them. We run 5ks because its been a standard distance to run for a long time. Other countries also do similar things, old habits die hard.
We use metric for science and medicine because the benefits of metric are much more pronounced for those use cases.
Honestly, using both really isnt that hard. Its only really an inconvenience if you aren’t already used to it. We aren’t changing it because we’re getting along just fine the way things are, and there are much bigger problems to be solved.