Economics. plain and simple. it would have to be designed tested redsigned manufactured, with a new clutch cover with waterpump and gear, radiator, mounting for radiator all hoses etc.probably looking at a final cost of $2500 $3000 and sold to a target audience with very little dsposable income. then you have to sell enough kits to recoupe your initial investment in R&D and tooling/mfg costs before you even make a penny profit, then you have and stock spare parts, gaskets, hoses radiators etc, then add to that the a high return rate since your target audience is young, mechanically inexperienced, will cut corners during assembly and tuning, then blow it due to airleaks and improper jetting and send it back to you screaming to everyone he knows that you make make and sell something that is a complete piece of sh*t.
laugh, biotch, whatever.. I have been told this exact thing by the owners of several aftermarket companies.
and this is why I have a bunch of precut peices of steel in my garage, along with a shiny new welder, and two precision jigs sitting in my garage gathering dust. I realized it would be cheaper to not make and sell a long travel rear suspension setup. I realized thru testing that you would not be willing to spend $1100 on a custom redisgned swingarm with a new shock properly setup and valved for the geometry, nor where you going to take the time to adapt and learn to ride a bike with long travel (it's a completely diferent riding style).
this is pretty much a direct quote form a PM exchange I had
"Hi, my son has your rear end setup and its way to soft and he is actually slower than he was with stock suspension, where can I get the shock redone to work better"
me: "your son needs to ride the bike differently with long travel, he needs to stand up and centter himself on the bike (like riding a 2 wheeler), the ONLY time he shopuld be hanging off the back of the bike is if he thinks he is going to die."
Dad" he said he has tried eveything and nothing works right, you said it would make him faster and he is slower, you have to have this shock redone"
me "there is NOTHING worng with the shock, please go out riding with your son, watch him ride, encourage him to move foreward on the bike and make the suspension work, work with him daily for 2 weeks FOCUSING on chaging his rideng style and then get back to me. I will not replace perfectly good parts)
Dad (three weeks later) good news, I worked with my son a you said, at firsthe was not comfortable riding that way but with a lot of practice he got the hang of it. He raced sunday and was passing 400's and the new 450 mx machine in the whoops like crazy and he not only won his class but beat most of the bigger bikes that were on he track with him, thanks for your help"