In the ideal world, you are right, computer systems should've been using TAI for time tracking and converted it to UTC/local time using TZ databases. But in th

In the ideal world, you are right, computer systems should've been using TAI for time tracking and converted it to UTC/local time using TZ databases. But in the real world a lot of systems made the wrong choice (UNIX being the biggest offender) and it got deeply encoded in many systems and regulations, so it's practically impossible to "just switch to TAI". So it's easier to just re-interpret UTC as "the new TAI". I will not be surprised if some time in the future we will get the old UTC, but under a different name.