Because you're 100% incorrect. Have you been to the production facilities in WI and TN? "Most who work on them?" Anyone can work on a simple lawn tractor, farmers do that in their spare time. Are you an engineer? Of course there will be a lot of similarities in design and function, especially in this day and age.
AFAIK John Deer do not make anything smaller than about 2 tons.
As a mower mechanic I am under them all the time.
The frames on the 100 series are not "similar" to the AYP frame they are identical right down to all of the holes punched into the side rails making them weaker for all of the parts that JD do not fit. Every hole punched into plate add about $ 2000 to a press die so no one in their right mind would add 42 redundant holes to a die.
At the very least, the mainframe pressing , cross member casting, wheels, rear fenders pressing, instrument turrent pressing, PTO lever & housing, brake & motion levers are all made at AYP then shipped to a JD plant for assembly
However if JD was doing that for all their lawn & garden range they are loosing money on every 100 series they make.
The only part that does not interchange is the actual deck itself, the real deck lift arms and the fuel tanks, although you can fit AYP tanks into JD's I do it all the time as the AYP tanks are better.
Not having been to any JD factory outside Aust I can not vouch for what goes on in every USA JD factory, perhaps they do have a tit for tat deal with AYP similar to what they have going with sub compact tractors where JD make the top end AYP's and AYP make the bottom end JD's
Note I did not say they are a rebadged Husqvarna's, the main frame is a heavier pressing as are the body panels and the pedal pivots go through hexagonal holes with plastic bushes in them, right next to the plain round holes where the AYP mower axels pass through the frame unbushed.
Prior to going broke Murray made some JD small equipment as Murray have paint codes for JD Green & JD Yellow
Lawrenceburg paint codes
E011 J D Yellow
E511 J D green
Jackson / McKensie paint codes
- 831 Scotts Orange
- 857 J D Green
- 858 J D Yellow
The petrol powered D series ( note not the D 100 series ) and the LX series were made by Honda and they have an alloy tag on the frame rail stating John Deere and a decal near the rear wheel stating "manufactured for John Deer inc by Honda America".
I do warranty work for a local JD dealer and down here JD are substantially cheaper than most other brands because they piggy back the lawn & garden stock on the farm & construction logistics & warehousing so at least 1/2 the mowers I work on are JD mostly the 100 series. The closest big dealer sold Husqvarna so again I work on a lot of them and I fit a lot of JD parts to Husqvarna's because the JD parts are cheaper.
The diesel sub compact tractors are rebadged under a deal where JD make the bigger tractors for the same companies that make their branded smaller ones.
This is a standard manufacturing proceedure as it is not economic to make everything yourself so you make what you can make a profit on for yourself and for your competitors and they make what they can make a profit on for themselves and for you.
If the auto industry did not do that every USA plant would have closed down in the 70's when they became uncompetative against the Japanese & Korean factories.