How does room sharing prevent SIDS?

We follow all guidelines for safe sleep except room sharing. I know that room sharing prevents SIDS but it’s not clear to me the reason. Is it just because of proximity that we would be close by if something were to happen? Is there some other scientific or biological reason for room sharing that prevents SIDS?

Our bedrooms share a wall in our fairly small house, it’s even likely that the steps it takes for me to get out of bed and walk to her crib is less than other’s who have a larger bedroom and are room sharing. We have a video monitor with the sound on, though we can hear LO just fine without the monitor. Also we take shifts as our work schedules are nearly opposite each other, so somebody is almost always awake when baby is sleeping, and we’re always ready and able to get up as soon as she needs us.

What’s the reason behind room sharing preventing SIDS?