Why not indeed.
Consider what it is that you are calling a ‘drawback’ and your inflexibility for using current tools that the developers have already provided.
In a similar way, but on the flip side of this realm population equation, the players in (for one reason or another) smaller communities have to deal with not having enough people online to access all of the game’s content. That is their drawback. Years ago, Blizzard reassured us that they would be faithful stewards to these Era communities before the tbc launch:
Yet they have gone on to develop a season and numerous expansions without further intervention. They’ve neglected their duty.
These players now also have to deal with users that contribute nothing to the small realm’s community and continually exploit the free transfers service to fuel activities on the larger realms.
Your request to fix this minor annoyance here would effectively nullify another natural and legitimate reason for players to migrate. This would further alienate players with far greater and longer-standing in-game complaints who’ve been patiently waiting for Blizzard to stop ignoring their petitions.