Why do several countries have obvious gaps in their SIM ground battle rosters?

The title should be relatively self-explanatory. As many others have previously said, the ground SIM lineups make very little sense quite often. Some countries suffer from this much more than others. China, for example, was missing their 8.0 Type-59 and Type-69 in the previous (at time of writing) cold war bracket. At the same time, in the very same bracket, the USSR had three 8.0 T-54s.
Although this current top tier bracket is slightly less egregious, there are still strange vehicle exclusions: Russia, Germany, and the United States all receive both their Senrai premium tanks and its non-Senrai premium equivalent, yet Britain and Japan only receive the non-Senrai tank, while China gets neither their Senrai MBT-2000, its pack equivalent in the Al-Khalid, nor the tech tree MBT-2000, all of which (at 11.7) would fit squarely within the current BR range of top tier SIM.

I would greatly appreciate anyone else’s input and suggestions to remedy this seemingly easy-to-fix oversight.