Forty big blinds is a different game
The rule
A short stack is not a deep stack played carefully. It is a different chart.
Speculative hands are worth what they can win when they hit. Small pairs and suited connectors miss most flops and pay for themselves on the rare ones where they stack somebody. With forty big blinds behind, there is not enough left to stack anybody, so the payoff those hands are priced for never arrives.
So the range tightens toward hands with immediate strength: high cards, pairs, hands that are simply ahead when the money goes in rather than hands that might get there. The same reasoning keeps going as the stack shrinks, until eventually raising and folding costs more than moving in did.
Read more: stack depth, implied odds