It's most likely a kit that only uses freewheel compatible motors. THey offer to sell you a 7 speed 14-34T freewheel for $5.
I personally keep the 3 speed front derauilleur on conversions. On one bike, I had to change to a 6 speed freewheel because the frame was too narrow for a 7 speed, but most of the time, you don't need all the gears with a motor. What you will miss is that Shimano freewheels only go down to 14T. DNP does sell a freewheel with 11T, and you will probably want that to avoid spinning out the pedals at higher speeds.