Hackett said the salarians were attacked after Thessia, and that they are putting up a "spirited defense". Salarians and Asari definitely fared much better than Humans and Turians. Even if we assume the reapers conquered Sur'kesh, it spends a lot less time occupied than Earth or Palaven.
This.
Intro arc - Nothing
Genophage arc - Perimeter maybe being tested, but nothing happening
Rannoch arc - Perimeter maybe being breached, but nothing huge
Thessia onward - Perimeter breached and Sur'Kesh in danger of invasion, bringing all the major species into the Crucible fold
I disagree with Massively - I think they were eventually invaded, but Sur'Kesh is not nearly in the same shape as Palaven, Thessia, or Earth. Around the end of the game, it'd be just starting to get invaded, if that.
The Reapers likely don't attack Sur'Kesh until near the end, because the Salarian advantage is striking first and knowing all about the enemy. Because they were unable to do either, the Salarians get to sit on their superior-minded asses and just hope that they'll make it. Once their Councillor is attacked though, they have no choice than to send at least a fleet to support the Crucible plan. It is this movement (and likely similar things), that would have brought the Reapers finally to Sur'Kesh near the end.
The Reapers have goals, aims, and strategy. The Salarians are the weakest in the type of conflict against the Reapers, and of less priority. The Turians are the biggest combat threat, and the Asari are the biggest leadership threat. The Salarians' science matters little while the War/Harvest is going on. At most, they'd be able to figure out a significantly useful Reaper weakness at some point later on. It's not that the Reapers were avoiding them - it's that resources are better spent elsewhere at first.
Heck, they even underestimated the threat of the Krogan, Quarians, and Geth - just sending one Destroyer to each home planet and seemingly calling it a day.
But then Shepard and co. interfered and forced the Reapers to divert forces to keep those species occupied. The end result is that the brunt force of the Reapers are still on Earth (and still very invincible), but spread out more than they might have liked and left an opening for the Crucible to work its magic instead of being immediately destroyed. At least that's how I see it.