The thing that makes Aedes aegypti such a good vector is its tendency to feed on multiple humans. They get spooked and fly off from a feeding site, then land a

The thing that makes Aedes aegypti such a good vector is its tendency to feed on multiple humans. They get spooked and fly off from a feeding site, then land again to try again, and the subsequent bites might not be on the same human. So one infected mosquito can vector a disease to an entire room of people if there is enough activity to make them attempt that many bites. Many other mosquitoes will just stick it out and hope you don't notice them before they fill up. They either succeed in one bite or get squashed. Those mosquitoes have less opportunity to acquire a disease from an infected human, and less opportunity to transmit one to an uninfected human. And if there is no mechanism for that vector to pass to a mosquito's offspring, the one-bite behavior means there is no transmission between humans at all.