Linked from
The 10 pages that link to Import quota, each with the reason it gives.
Free tradeRelated: Quotas restrict trade by quantity even when tariffs are absent.
ProtectionismRelated: Quotas restrict foreign supply directly rather than taxing it.
AutarkyRelated: Quotas directly restrict foreign supply as part of efforts to reduce dependence.
Trade liberalizationRelated: Removing quotas allows imports to expand beyond a fixed ceiling.
Balance of tradeRelated: Quotas directly restrict one flow counted in the trade balance.