That can be difficult to call. I've tried to base it on if the show is primarily about having a laugh as opposed to primarily being about the competition/discussion and laughs also happen. Have I Got News For You and The News Quiz are mostly about being funny rather than the answer. A Question of Sport is more about the sport's knowledge/competition even if it can also be funny. Call My Bluff, whilst containing humour, could also have non-comedic definitions for words. As humour is very subjective, and everything doesn't fit into neat binaries, you may disagree on some classifications.
In short, because that is a constructed convention from some time around the 1930s. It is unhelpful. I wanted two other colours and my friend suggested green and purple. It happens that they are also the colours of the Women's Social and Political Union so that is a bonus!
Because gender isn't binary. So I built in the option for people who don't identify as either male or female. The gender information is stored on an episode-by-episode basis to cover people expressing a different gender at different times in their life. If you have been on one of the panel shows and I've mis-gendered you at all, please let me know and I'll fix it.
Having an other category also allows for appearances by groups where the people who make it up are not individually known from the listings. There are also two instances on Have I Got News For You where non-gendered, non-human contestants were included.