User blog comment:AdmiralPedro1stFleet/How to Explain Absence of Geth Juggernaut and Geth Hoppers/@comment-2250460-20120303000533/@comment-1388547-20120303002737

Indeed -- they may simply not have been part of the force composition the geth happened to bring with them. Though the hoppers might also count as a bit of a failed experiment, since they were fairly easy to counter in ME1 using biotics. I'll be interested to see what new nasty surprises the heretic geth have in store for us in ME3.