2010 Chevy Equinox drive system

There are 2 ways that can happen. First, the wheels with least resistance will spin first, so all 4 wheels would have to have the exact resistance for all of them to turn (unlikely).

The only other thing is quadra trac. Jeep uses true posi traction front and rear differentials which will give you true "4" wheel drive. All others will usually spin one front and one rear wheel in poor conditions.