I’d be surprised if Sony handed down some edict to “go dark”. Probably the studio wanted to explore something different.
It’s a shame though. I adore Precursor Legacy. In my mind it’s a brilliant 3D platformer in the style of Nintendo and Rare. Jak II was a pretty significant step down and the series was never the same. If you had asked me in 2002, which series would end up better—Jak or Ratchet—I would have bet everything on Jak. But it fizzled out while Ratchet on PS2 got steadily better with each installment.