Probably no-one at Apple noticed because they're all still using the command line instead of Disk Utility for everyday volume maintenance, and the bug isn't present in the command line version. Everyone uses command line diskutil because several versions ago (I think in El Capitan) Disk Utility lost essential functionality. If, for example, you wanted to set up software RAID (e.g. mirrorring) you suddenly had to use the command line. If you've been routinely doing that for two years or more and you're a developer, of course you're going to continue instead of learning High Sierra's new Disk Utility.
The real disgrace is that El Capitan ever got out the door with that neutered Disk Utility. Lots of people in the creative industries - photographers, video editors, animators etc. - had a need for and used RAID, especially with the popular cheesegrater towers. To expect those kinds of people to use the command line was absurd.
So this isn't just a matter of poor QA on High Sierra - although it is that - but poor software development plans as set out by senior management. It was a conscious decision that power users, including Apple's own developers, would not be "eating their own dog food".