Why is the VLS launch system considered better than non VLS. What are its advantages?

VLS as in Vertical Launch System?

Well that's obvious, the ship doesn't have to manouvre into position when firing the missiles, it just fires them straight up and they fly themselves onto the right course.

Generally speaking those missiles are also better protected from outside influences.

yep.

also, you have to look at the other points too.

(1). vertical storage: better utilization of the adaption of the narrow hull versus storage space for weapons.

(2). weapon advancements: the box they are stored in can be rapidly redesigned and or removed for the emplacment of a improved system.

(3). Visual attractiveness: the launch contrails look so much better going up than out...

Another reason: big external boxes make big external targets.

. . . is rate of fire (Along with the other comments). A non-VLS system would require the launcher to spin back to straight-up after launching the ready-missiles, missile(s) to be rotated in the magazine carousel under the launcher, and the missile(s) elevated up from the magazine to the launcher arms . . . all before another pair of missiles could be sent on their way.

Restocking would undoubtedly be easier, since the missile boxes could be lowered down into the VLS magazines, instead of placed inside an underdeck carousel.