Problem is with 100% code coverage of badly guarded / implemented code you'll have a fall sense of security if you're just looking at coverage as the metric of quality. Anytime I've worked with a company who had a required code coverage percent, they never actually cared what the code being covered looked like only that it was covered in some test.

Without going down the rabbit hole of Goodhart's law, code coverage % is a poor metric particularly when used standalone.