Jarmel said:Well considering they had to completely change their modus operandi, it actually makes sense for them to go in force and wipe out one planet at a time. If they tried to spread out 1 ship at a time, the combined Council fleets might be able to chip away and wipe out each Reaper but as a whole, nothing could stop a combined Reaper armada.
Also it seems that not every race can produce a Reaper which explains the Collectors as the Protheans couldn't produce a Reaper.
No you go after the Citadel and cripple the whole galaxy at once.