IIRC it was investigated by gnif (resident server maintainer) and it was not as trivial as you make it out to be, and most decided it wasn't imporatnt.
No other forums I'm on use https
Hardly anyone is asking for it, not a single person has quit or refused to join the forum because it doesn't have it, and quite frankly not moving to it is one less thing that can go wrong.
It's clearly a feature some (including myself) would like to see implemented as it's been brought up a number of times. Saying no one has quit or joined is all well and good, but it's almost impossible to provide stats on that unless they tell you. As for another thing to go wrong, normally I'd agree with you, but it's old technology that is been tried and tested. I personally believe the benefits outweigh the off-chance something was to go wrong.
Maybe gnif can weigh in on the conversation since he knows the server and site set up intimately. I suppose it's one of those things, once implemented (even if it requires a bit of work to get there) can be left alone to do its thing for the mid-to-long term.
I'd have to say, 90% of the websites I visit use HTTPS as standard, including news sites, hell even porn sites.