Leave aside all the puffery about 3-1 and such, you described a front wheel drive (pull) walk-behind (FWD), but are asking why the rear wheels won't propel. When you push down the hand grip the front wheels should spin free. Whan you lower from wheels by releasing pressure on hand grips, turning wheels lowered to ground should propel the mower along with its unpowered rear wheels now turning be ground contact. Reminder, never, ever lift rear drive wheels of any mower off the ground while walking behind with engine running:
You could be struck by blade propelled object.
You could pull mower and spinning blade backward onto your feet.
You could lose balance and be pulled forward in a fall.
Contemporary FWD mowers are recognized by a black chain housing on deck top leading from engine to left front of deck. RWD propelling chains are situated underneath deck so cannot be seen from above.
Have you had your wheel bearings checked. With the front wheels straight, back up about 50 feet then pull forward about 50 feet. You will need to do this on level ground. Then from about 25 feet in front of and behind see if any of your wheels look like they are tilting in at the top. If so jack that wheel off the ground and see if it moves in and out at the top. If so its likley the wheel rubbing aginst the backing plate of your disk brakes. Let me know what you find