>>55349664The data structures for 3 / 4 are drastically different, just going from 3 -> 4 (and 4 -> 5) already has a ton of data loss and assorted instances of corruption. Maintaining identical data structures between generations would have prevented the series from progressing and innovating with new games (with the most notable example in 3 -> 4 being the removal of ability hardcoding)
What there isn't any reason for, however, is why you can't backtrade from 7 -> 6 when they use the same structure - or even 8 -> 7, for that matter.
They finally allowed it with 9 -> 8, but at this point in the series the pokemon structure is actually stored in a super lossy format - half of the information unique to the Pokemon is actually stored server-side and is reassigned each time you move the Pokemon into a new game. And even then this is still lossy and corrupts metdata when going from 8 -> 9 -> 8 lol.
