There are two likely reasons that the gear is likely to be left down.
1. The journey is short, so not worth it.
2. The maximum airspeed for lowering/raising the gear is 80 its, so if you're whompiting along at max chat, it may be thought easier to leave the gear down. (Yes, I know you have to slow down to land so why not do it then).
There are of course other reasons but for the cases pointed out, these two are my best guess.