Front tires spinning in 2wd

So I just bought a 2015 scrambler and I just took it out over the weekend and I rode around in 2×4 all day, but I noticed when I was doing water wheelies the front tires were spinning even though the switch is in 2×4. If I switch it to AWD it’s a little harder to steering going slow so I know it’s locked. Can someone explain this to me