The difference between 80% coverage and 100% coverage is overrated. 80% is more than sufficient, i'd even go ahead and say 70% is better.
100% goes into "change detecting test" territory. There's also the time aspect: going from 0-70 is not hard, 70-100 is extremely time consuming, and often not worth the effort.
Monitoring is a way more efficient tool at catching issues.
While I agree with 70% is about the sweet spot, it really depends on the tools you're using.
We've found that with using Jest and just doing snapshots you can get to 70% without actually testing any of your others methods, hence the 80% coverage requirement.
That being said, we do something similar where we require 80% coverage.