Just imagine what it was like when I was saying you didn't want it yet
Sure, you could "fix" that in one minute, but then you'd instantly break tens or hundreds of thousands of applications that do weird shit with window chrome.
There are improvements coming to make modern app chrome more consistent with win32 app chrome, but it's anything but simple. If you make modern apps chrome smaller to make it consistent with Win32, then it's less touch friendly. If you go the other way you make major breaks with back compat of applications millions of people use that would likely never be updated.
What you're suggesting is obviously the first thing the shell team tried, and then rethought plans when they discovered the consequences.