Makuta’s big plan was to bring Mata Nui close enough to death so he could possess the Great Spirit Robot, then be revived by the Toa. Why, then, did he bother implanting the Mask of Life into the minds of the Piraka when the whole goal was for the Toa to get the mask? It seems like he’s just putting an unnecessary obstacle in their way.
I think it’s a combination of factors. If you recall, Zaktan had stumbled across the entirety of Teridax’s plans underneath a old Makuta fortress the DH’s were occupying. Zaktan saw it, and made sure he was going to involve himself in the plan, so he could profit.
Teridax more than likely involved himself so he could manipulate how the Piraka went about inserting themselves his plan.
(also, nice pfp, humanized takua)
Bought Makuta’s Guide to the Universe and discovered the answer - Makuta needed to delay the Toa long enough to ensure he could possess Mata Nui’s body.