Scotchguarding should last 5-6 years of moderate use and should not be affected by cleaning. That is, IF IT HAS BEEN DONE IN THE FIRST PLACE!
There are many instances of retailers claiming suites have been protected, charge considerable sums for it and give the impression that the suite will stay clean as a result of, protection
As Chas' says, it's more likely to be th material, that's scaring them, possibly a non woven synthetic, which has the potential to delaminate.