I fly the Ozone Instincts, on water and snow,
and I always keep my lines attached when packing up my kite.
5 lines make it a little harder,
you just have to be sure not to get the lines inside them self (twisted)
4 line kites are
I think the main reason most don't keep them attached,
is they may use the same bar on other kites.
But mainly, it's a habit, or monkey see, monkey do, thing.