There used to be a time when a chap bought a roadster, tinkered with it to make sure it was "on song" then spent the afternoon honing around the countryside without a care in the world. Their cars were often affordable toys, or something a bit special.
However, as time moved on there was been a shift in what it means to drive a " fun" car. It has to work, flawlessly, all the time. It's also to be do more than just be a bit of fun, as most houses don't come with free parking any more, so you need to have something that has and does pretty much everything -- space, pace, and maybe even good looks.
For some, roadsters are still a viable option -- the Mazda MX-5 wouldn't exist if people didn't want a bit of open-top fun. However, they have a bit of an image crisis. Many people see them as a more feminine choice, which means men aren't going to buy them. This may be an issue for Mini, as they see the Roadster Coupe as the more masculine cars in the range.
Minis are always a good giggle to drive, even the Countryman is so fun to drive (yes, yes it is) it's a giggle. The Cooper S is fast, too, so you won't want for speed. And, yes, I think it looks good. Though maybe a touch like the Mini Hatch has been scalped, but still...it looks good. It's certainly something I'd smile at if I saw it on the road.
But it's not the super-masculine car Mini wants it to be. It doesn't look like a purposeful sports car, it doesn't give the impression of "Man make speed. Ugh."
It's also not a hot hatch, which can come with similar performance, more muscular looks, and can fit more people and things in it.
All told, though, it doesn't matter what anyone thinks of a new Mini. People will buy it regardless.