Why is the blower fan not rotating in reverse upon reversing voltage?
The way to turn a centrifugal blower into a vacuum is to attach a suction duct to the center port. There is no other way, reversing the motor won’t work.
This is because this kind of blower works by accelerating air radially, from the impeller center to edge into the ‘scroll’ (volute). It doesn’t matter so much which direction the impeller is spinning, radial acceleration still happens, although it will be more efficient in the preferred design direction than in reverse.
The inverse of a blower is a turbine: high-velocity/high pressure air enters at the edge into the volute, which accelerates the impeller from edge to center, leaving the center port at lower pressure and velocity. Combine the two, and you get the main plot device for a cheesy Vin Diesel movie franchise. Or a reason to buy a certain Subaru.
Anyway...
You asked why the motor didn’t spin.
In this blower, like most low-voltage DC fans, the motor is brushless DC. They do this to increase the life of the motor. Brushless DC fan motors, unlike brushed motors, are designed to work on only one input polarity because the supply powers the control IC and drivers, and it’s only required to work one way.
You may have fried it by connecting it in reverse, or if you’re lucky, the controller board had some built-in protection.
At any rate, as you saw, the motor didn’t spin.
Is it possible to make a reversible fan? Sure, an axial type with a brushed motor, or a BLDC with a reverse capability could do that (if they existed) by changing the phase sequence to the motor coils. That’s basically what a ceiling fan does, be it an older AC motor or more modern brushless DC type.
But not this fan, which can only do suction at the inlet and pressure at the outlet.