(This is tentative.)
The reason we feel threatened with suffocation when reading the Philosophical Investigations is that it seems to point to no “outside”. The Tractatus seemed to have an outside.
Even the fly in the fly-bottle – if he knows he is in the bottle – has an outside, and an outside can be both an object of hope or one of despair.
Hence, perhaps, the “lack of hope” one can feel: it comes from the reader’s metaphysical intuition that change is something coming from the outside to the inside: if there is no outside, no change is possible.
Perhaps – once we are outside the fly-bottle, or imagining ourselves to be – we only feel trapped because we mistake “having no outside” for “our outside being somewhere we can’t get to”.