Even if Loblaws had some ultimate purpose (redevelopment, perhaps, although seems premature in the case of the Coxwell store), it doesn't make a lot of sense for them to suddenly close the stores and to generate no revenue.
The trend here is that these No Frills stores are operating in really old grocery stores that have seen little investment over the years in the bones of these buildings. Some engineer is probably telling Loblaws that there is a liability/danger here.
ETA: Loblaws did recently make building permit applications for the Coxwell store - in addition to the one shown below, they've also applied for mechanical and plumbing permits.
View attachment 93836
that smacks (to me) of a serious systemic problem in property maintenance.
The failure to be forthright w/the public about the nature of the closures also adds to the speculation.