Why is the placement of the series resistor in data lines important?

The purpose of a resistor placed here is not to limit (or limitate) the current, nor to increase the rise and fall time of the signal (though that's what it would do if it were feeding a lumped capacitor).

The purpose is to match the source end of the transmission line formed by the track. This means that when the unterminated far end of the line reflects the signal, those reflections will be absorbed in the source resistor, resulting in a clean signal received at the far end. Without that resistor, there could be multiple transitions at the far end, distorting the signal.

Not considering what Neil_UK tells us (which is likely to be more relevant than this) - it would still make a difference for a simple reason:

The resistor will divide your line in two parasitic capacitors. If you place it close to the source, you will have a "large" parasitic capacitance behind the resistor and such the time constant will increase for the receiving side.

If you place it close to the receiver, you will have a large parasitic capacitance directly connected to the source, which will charge nearly instantly. The capacitance on the receiver is now close to the input capacitance of the pin you are toggling, so the time constant is smaller and you don't get as much smoothing.

Depending on the layout this effect might be negligible, but you can get some picofarads quite quickly and they might matter.