Did simple input signal for IGBT, MOSFET or output signal from stepper chip work without pullup?
No because the IGBT, MOSFETs etc channels only switch to ground, so you need a power feed, and you need the resistor in there or when the thing switches to ground the current will be massive.
The way it works (sorry if people already understand this) is that when the channel is closed the tacho sees ~12v on its trigger line, then when the channel opens the voltage drops to zero, then back up to ~12V when the channel closes again.