Part of it is that you are not their only support network; many siblings offers many outlets and sources for help / support / etc.

Running a family that large is also certainly more time consuming in some aspects- grocery shopping is a significantly different experience when you go through multiple gallons of milk and dozens of eggs every few days, as an example.

You rely on older children to help, and the whole family unit functions as a team.

A good friend has 8 siblings. My parents both had 6. I only have the one, who is several years older than me. The family dynamic between a small and large family is simply fundamentally different. That doesn't mean less emotionally attachable or available, but almost certainly less one-on-one time.