My guess is that with many of the members on this site, they've essentially "won the game" to the point it really doesn't matter if the mortgage is paid off or not. It basically comes down to "do you want to win by more?"
Even in my situation, I don't think it really matters whether I pay off the mortgage or let it play out til the end. The principal/interest portion of it is about $1941/mo, and I owe about $438,000. I can either keep paying the $1941/mo, and let that $438,000 keep working for me. Or cash out the $438,000, to get rid of the $1941/mo payment.
My mortgage is only 2.875% though, so financially it's probably worth it to keep it, at that low of a rate. I also itemize on my taxes, and at this point in my life, that mortgage is giving me over $1,000/mo to write off. I also don't have $438K just lying around in petty cash, so it would involve selling some stocks/mutual funds, which in turn would trigger taxes.
Still, even if I decided to pay off the mortgage, to get that peace-of-mind tranquility of a paid-in-full house, it wouldn't ruin my chances of financial success. For me, and I'd presume many others, it's not like one decision is the clear winner, and the other is destined to make you fail.