Maybe this helps: I spend every year almost a month in Florida together with my family. We usually go there around end of february or beginning of march because it isn't that hot and we can still enjoy a warm weather and warm water.
Sometimes however it is very hot outside, especially in the Miami/Fort Lauderdale area. Our hotel in Ft. Lauderdale is pretty good and a lot of cabrio drivers stop there to spend a few nights for a business meeting, vacation or just to take dinner at the nice restaurant. I always observed that the soft top was closed and I didn't understand. So when a nice couple got out of a Mercedes SL 500 together with a 3 year old kid, I found the courage to approach them because I was with my daughter too and I thought this would be a good "excuse" to ask them. They both were very nice, we even have eMail contact and the woman gave me a simple explenation: when it is very hot, they drive with the soft top closed because they enjoy the A/C. Especially when they go out or when they go to work or a business meeting, they don't want to be wet allover and/or have visible sweat stains allover the dress. I started to understand.
So maybe this is the reason: if people drive to work in a Cab and it is very hot outside, they prefer to have it cool and get fresh to their work. I always enjoy driving my wife's SLK 32 with the top opened but I went to my office once and was wet allover. My back was so wet, there was a huge dark sweat stain visible (I had a dark olive coloured shirt on) and it looked horrible. Never again.