Help understanding the wiring in this electrical box

I am working on adding outlets to my garage and decided to open up this strange double switch box that is 6 or 7 feet up on the wall.

There are two separate circuits in this box, one that the kitchen and dining room lights are on, and one that the garage lights and existing outlets are on. From top left to right:

• Cables 1 and 3 are on the dining lights circuit (cable 1 is the power feed, hots were already separated in this pic)
• Cables 4 and 5 (bottom right) are 3 wire cable and part of the 5 way switch wiring for the garage lights (lights can be switched on and off from 4 different locations).
• Cable 5 is the one bringing power into the box, where the travelers (black and red) are spliced to the black and red from cable 4.
• The white from cable 4 is bundled with the other neutrals in the box (which includes neutrals from the dining lights circuit), and the white from cable 5 (power) is connected to the black from cable 2.
• The white from cable 2 is part of the neutral bundle.

As you can tell from my description, I was able to dissect the box and identify the cables, and I successfully replaced the box and connections properly and everything works. But… I am confused about the wiring on cables 2, 4, and 5. Why is cable 4 picking up a neutral in this box? And why is cable 2 being powered off of cable 5? Lastly, is it appropriate for these two separate circuits to be sharing neutrals? I hope you are able to follow my post, I know it's a lot to read. Thanks in advance.