Then explain what quicken spell metamagic should do, if not let you cast additional spells? You're limited as it is.
In DnD you cannot cast 2 level 1+ spells in the same turn.
Quicken spell allow you to cast a level 1+ spell and a cantrip. Or a fireball as a bonus action then a regular action... but not 2 fireballs / turn, which would be pretty OP
