The laser array is expensive but if it's continuous and spread out enough you could keep sending newer probes. Or if it's not continuous you could use it for different directions!
According to Scott Manley's video on the topic the probes would need to arrive at the correct time in order to form what is effectively a huge phased array antenna.
Only then is the combined transmission power of these tiny probes large enough to be received on earth.
A very cool idea, however the headline is misleading - NASA has not even remotely committed to running this mission. They've selected the swarm project as one of 13 projects in their innovation program and given it up to $175k to study feasibility. That's roughly a postdoc for two years. This is far, far from committing the hundreds of millions or billions needed for the execution of this mission.