Full frame Pentax

Why everyone asking for FF? Why not to buy wider lenses?
Why nobody asking for a reliable flash metering, fast autofocus from Pentax? At moment I considering Nikon 600 or Canon 6. But not for FF, but for latter reasons. FF just for the reason, that prices are close to a crop sensor. I do a lot of shooting job indoors with a low light. But Pentax will stay No1 for travel photography.