I thinkkkkkkkk.......(here we go...)
In the concept stage, the producers were so determined to show that this show wasn't just going to be TNG Mk 2 (or TNG: the next generation indeed) that they latched on to this "ship alone" idea without really thinking through the decision.
We learnt from the 7 years of the show what they really wanted to do was TNG with a new set of characters and new sets, so marooning the ship in the delta quadrant was probably the biggest mistake they made.
Only a few episodes dealt with the isolation aspect so it obviously wasn't a concept that interested them too much bar the first year publicity they could milk for the show.
The Maquis, too, was an idea they quickly fell out of love with.
But the "divided crew" motif again made it initially appear different enough to TNG to be useful when launching the show.
The way it turned out, they might as well just had the Enterprise D decommissioned and give them the Enterprise-E, have it on a long term mission exploring the non-Dominion parts of the Gamma Quadrant through the wormhole etc but still able to pop back to the Federation for resupplying/shuttle restocking
that way you get the best of the "ship alone" aspect and also not have continual questions about how this ship isn't running out of power/shuttles every week.