Couples that follow the tradition of one breadwinner, one homemaker don't necessarily need work authorization (if the USC is the breadwinner). Yes, I know that's very last century, but it's what the K-1 is designed for, and that's reflected in other ways too (such as needing evidence of approval of families). In such a situation the faster arrival in the US means less time supporting separate households and less travel, which can make the K-1 more cost-effective in total despite the higher fees. (That does assume that K-1 is faster processing than CR-1, which is not guaranteed and varies with agency priorities, but for traditionalists, having that processing overlap with the engagement period also is a benefit)