These are all reasonable reasons for him to be whining. (caninejournal.com)
There are some good and very reasonable reasons to have both parents on site. (gsdca.org)
That TL; DR is the core of the answer - it obviously makes sense, because they get more money that way, and the only reasonable reason not to do it would be if they couldn't - thus, «because they can». (money.stackexchange.com)