Because they are lazy and are not aware of the prior work.
Already decades ago many have proposed to use only TAI internally in computers, instead of UTC, which is not a time.
UTC should have always been used only to compute the local times, together with the time zones, only for human interfaces.
There have been for decades libraries for using TAI instead of UTC, and even versions of Linux or *BSD kernels patched to do time keeping in TAI, not in UTC, eliminating all problems with the leap seconds.
Unfortunately the use of TAI has remained a niche, but that was the right solution.
Already decades ago many have proposed to use only TAI internally in computers, instead of UTC, which is not a time.
UTC should have always been used only to compute the local times, together with the time zones, only for human interfaces.
There have been for decades libraries for using TAI instead of UTC, and even versions of Linux or *BSD kernels patched to do time keeping in TAI, not in UTC, eliminating all problems with the leap seconds.
Unfortunately the use of TAI has remained a niche, but that was the right solution.