1) Gaara's sand is fast enough to block Amaterasu, which is an instant attack that even the fastest shinobi can hardly avoid. Shinobi that would have a field day with Toph.
2) Gaara's chakra reserves are much larger now he is an adult, you based this battle off of his kid self's chakra level. Gaara doesn't use the Shikaku's chakra, so he can literally do five times the amount described before running low at all on chakra.
3) While Toph can sense where his sand is at all times, so can anyone with eyes... including Deidara, Sasuke, Kidomaru, Lee, etc... they all at some point, have been encased by Gaara's sand. Each of them are much faster than Toph could ever imagine. While she may be aware of the entirety of his sand's location, she can't physically avoid it, she's simply not fast enough.
4) Toph couldn't have known that Gaara intended to crush her with the sand, she has never witnessed a tech like that one, so how would she had known to cover her entire body with metal, that happened to be able to withstand the force that Gaara uses to crush people?
5) If this was a known death battle, then Gaara won the moment he caught Toph the first time. When Gaara intends to kill, he does it the first time he catches the victim. Even if he chooses to toy with them, he will at least break an arm and a leg. Toph would had died the first five minutes of this battle or been injured right away and been unable to avoid his abilities at all.
6) Gaara is much smarter than you think and can come up with plans to outwit even the most powerful shinobi, Toph's intelligence feats are not that great. She accomplished everything due to her superior earth bending. Not to mention Gaara has went face to face with gods. Toph has no feats even remotely comparable.
7) Toph can't get close enough to hit Gaara, because his sand still protects him and Toph isn't fast enough to get around it at all. She would have to bend her way through it, which would allow Gaara more than enough time to knock her back or fill her body full of sand.
Thanks for the post below, I totally missed those points as well~
He doesn't usually resort to physical prowess, but he is still a ninja. he still knows the shunshin, the replacement technique, and many more. He can fly at mach speeds with his sand. I'm not saying that he should win, but they took this a very wrong direction.