TFT Resistive screen made multitouch?
It's a hardware limitation. Resistive screens measure the resistance from the top and the left, and bottom and right of the pressed point, and derive X and Y coordinates from these.   



Pressing two points simultaneously can't give you multiple coordinates. It can confuse the controller, however, resulting in a complete irrelevant set of coordinates.
No matter what technology, to get multiple sets of coordinates you have to scan the grid, looking at one point at a time, which resistive doesn't.  

The application schematic for the MXB7843 touchscreen controller shows the electrical model of the touchscreen as the 4 resistors on the left.   



When you are looking at the image you can see that it only has physical inputs for one point so asking for two is just not there.