two stall strips on different sides of the nose would be perpetually in "stall" and increase drag.
Remember that in the motorcycle case, the "wing" is vertical, and folks are putting a, more or less, vertical stall strip all along the nose.
This reduces the lift (which has a sideways force on a bike) generated when there is a change in the wind direction, regardless of what caused the change in wind direction. You still have side pressure (which is where cross ventilation or step-through is helpful), but you don't have
induced "lift". I put lift in quotes in case it isn't obvious that this lift is acting sideways to try and lay the bike down, and not trying to lift the bike.
the nose strip makes it act more like a flat-plate airfoil instead of an actual airfoil when the wind isn't straight on.
an airfoil can generate a much greater coefficient of lift at smaller angles of attack than a flat plate
We want the low drag of an airfoil without the "lift" ideally.