Why doesn't Also Bought recommend on a variant level?

Also Bought recommendations work on a product level. The app recommends products which were previously bought with a particular product.

Also Bought 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.