Why has the Perfect cuboid problem not been solved yet?

If I were to take a guess, I'd suggest that the reason it hasn't been solved yet is because there's not any apparent practical application, and nobody's put a bounty on it that's large enough to make it worth anybody's trouble to solve.

It's just not a particularly interesting problem. Apart from the romantic (and ridiculous) idea that Fermat had a secret proof of his conjecture that was lost to history, there's not much compelling about FLT aside from the fact that it's very easy to state. What makes it interesting is that Frey proved that given a nontrivial rational point on the curve $x^n + y^n = z^n$ with $n > 2$, he could construct a elliptic curve $E/\mathbb{Q}$ that isn't modular. That would be significant; it ties into Taniyama-Shimura, the Hasse-Weil conjecture, the Langlands program, and so on. Without it, FLT would just be another arbitrary Diophantine equation with mild historical interest, relegated to amateur and recreational math. The brick problem is not as elegant as FLT and doesn't seem to tie into anything more significant, so it's not a topic of ongoing research.