I think the clear answer is that there is no real reason other than habit and sunk cost fallacy.
There may have been some historical event that lead to this convention dominating over others (though I don't really know where to start lookin)
Klauen für die Wissenschaft? Die Terra X Kolumne
Recommendations for some easy to read 'feel good' fiction books?
Recommendations for some easy to read 'feel good' fiction books?
Massive Störungen: Bahnverkehr in der Mitte Deutschlands steht still
Massive Störungen: Bahnverkehr in der Mitte Deutschlands steht still
Hohe Kosten durch Deutschlandticket: Nahverkehr wird in den nächsten Jahren vermutlich deutlich teurer
The problem before was that it was impossible to not "contain" it if it goes right (at least with the previous sterilisation approaches), because a certain area got rid of mosquitoes too quickly, therefore not spreading that infertility wide enough, and then they just moved in again from other areas.