>>542337983
Every league has major balance changes and the current league mechanic is almost always retardedly powerful.
When a league ends, all characters in that league are sent to Standard. Standard is the dumping ground and a total unbalanced hellscape of retardedly overpowered player mechanics and a bloated economy. League mechanics can later go core (though not as powerful as their original state) and be part of the normal game experience.

For example, Crucible league added passive skill trees to weapons and all weapons that were created in Crucible league were sent to Standard after it ended. Crucible never went core for obvious reasons.