Several reasons ... its faster, often its all you need, it dont require any resources (i know its hard to imagine but if you are not hoarding everything you see, you can actualy run out of them
), it dont bother you with any cutscenes you dont really care about (and im not talking about talking with companions, you can easily skip that ... but turning night, raphael visit, astarion midnight feast, pissed of elf coming for revenge ... those events are unavoidable), immersion (you know the word people use so often around here when it suits them).
And many more. :P
When a game litteraly show a bridge between two location, there is only a bridge between two locations in this world.
May be ...
But how long is that bridge?
How long is that mudy road between the bridge and city gate?
How long is that mudy road between druid grove and the bridge?
etc. you get the idea
