Quoted from vdojaq:

I might be able to answer this? When I was a kid, I had just about every Hot Wheels contraption there was. I would go to neighborhood garage sales on my bicycle and buy any hot wheels track I could. Always, in every set up, a loop the loop or two, or three had to be involved. What I found out is that if the loop was too tight, the car would always come off the track. If the loops were too big, there wasn't enough centrifugal force to hold them on the track. My guess is between the playfield and the glass, there just wasn't enough room to make a proper loop to work without taking up too much space. The game would have been a one trick pony. Possibly a wire form cork-screw loop could have worked, but that is more roller coaster than it is Hot Wheels.
Again, rosh