There's this thing called "rain"...
What difference does rain make when it comes to keeping feet on flats? Flats have moved on from the potentially slippery blocks of rubber in the 60's!
I use flats, but they have pegs for good grip. I tried clipless but didn't get on with them for various reasons - mainly because I didn't like my foot being stuck in one position for all cycling activities (climbing, descending, fast, slow - all of which IMHO require small adjustments of foot position). Couple that with the foot cramps I got after anything more than 20 miles (OK I know the set up probably wasn't spot on, but I experimented and NEVER got it right) and I reckon any advantages were heavily outweighed. At my standard of riding, I am under no illusions about supposed performance gains in any case.
Often my rides also incorporate some other activity (pub, shops, visiting, eating etc.) rather than a simple home to home loop. I prefer normal footwear (and non lycra clothing too) for such activities.