Why doesn't Frequently Bought Together recommend on a variant level?

Frequently Bought Together recommendations work on a product level. The app recommends products that were previously bought with a particular product.

Frequently Bought Together does not recommend particular variants for each product. The variant selection is left to the customer:

There are various reasons for not recommending variants:

• As there are way  less  variants bought with other variants, there would be  less  products with automatic recommendations
• Not all customers select the same variants. For example, one customer would love a grey sweater with blue jeans while  other customers  would prefer a red sweater.