Why the limit on warranty to subsequent purchasor?

No one except those manufacturers know for certain what the reason is.
A shot in the dark guess is past experience has given those manufacturers a financial reason to exclude second/third owners. Perhaps the cost of repairing under transfered warranty the machines of second and third owners is more than they think they will lose on sales to "here today, gone tomorrow" customers who worry about the resale value of no warranty.
After all, the manufacturer only makes money on the first sale.
Plus, that also kills some of the incentive of dealer salesmen to buy at cost and resell as soon as they are allowed. A practice of very many audio salespeople. They get the product at below cost (as if they run demo's at home too) then the salesman only has to promise not to sell it for so many months... Ever notice all the just last years model poping up??? a bunch of those are these types. A non-transferrable warranty might help stifle that sort of profit taking on the part of audio salesmen.

I agree. I recently purchased an Audio Aero Capitole CD player and I am not happy that the warrenty is not transferrable. I did establish a rapport with the original purchaser(The Gentleman that I bought it from) and I believe that I can loop the thing back through him if I require warrenty work. I have nothing in writing here, just a very good feeling about him. Still, I would hate to have to try it. I purchased a very high-end McIntosh Amp that was only six months old at the same time and I am ecstatic that the warrenty is fully transferable.

Most people believe this is done to discourage internet sales. I believe this will backfire. Who will but a multi-thousand dollar piece with no transferrable warranty? No matter how much you like the piece, some audiophiles are always changing gear for whatever reason. A transferrable warranty is a big selling point. It is much easier to sell just about anything that has a transferrable warranty...

business here stays on the first place to knock off the used product lovers.
once the product sold new there is a need to sell another new and care less about its used price.

You are paying for the transferrable warranty. The company builds the potential future cost into the price. Many used buyers may not know the warranty is still good, since the manual or card is gone. The company profits more.

Since most gear breaks in the first year, or not at all, the company profit again.

If you want an example, go price a new Dell Computer online. The better the warranty you choose, the more the computer costs. Dell must make a fortune on them, because computers are usually DOA or break within 6 months; or they work until obsolete.