On the B737,one side is for fuelling,service and loading cargo while the other is for pax.
That avoids in my opinion pax being close to fuel leaks,some idiots are still trying to light up before entering the aircraft.(not all are as quick to respond as england ground staff
).
In case of fuel leak developping into a fire,the left side (half of total exits) can be used...away from flames and fuel leaks to disembark/evacuate.
The loaders are not allowed to whizz as you said under the wing nore to park there for obvious reasons.