There's IIRC a single-digit number of mosquito species carrying malaria and a slightly higher number of mosquito species targeting humans - as compared to hundreds of species of mosquito. Kill the carriers off and they just get replaced by some other specie of mosquito.

Lets face it, if the same Malaria mortality rate happened in the West, we wouldn't (and historically didn't) wait for vaccines - we'd pave over an entire ecosystem if we had to. We'd do the same even if we had the same death rate as the group that got vaccinated.