I regret that I can not change what.
Because we as an OEM manufacturer,
We need to obey the cost requirements of customers (dealers).
The cost is surely not the problem! This thing can be made much better without any cent more in cost. You simply have to exchange some values:

* Take 74LS244 Chips instead of 74HC244 chips! (HC chips are not meant for TTL interfacing. And the parallel port has TTL-Levels!!!)
* drop the 74HC14. It is useless. You can just put a solderbridge between pin1+2 to still have access to the "PWM Input" pins (although they are outputs, as mentioned...)
* Use at least 390 Ohm Resistors for the dir optocoupler (R16+R13) or even smaller ones.
* use 100pF for C1
* Remove R9 and the red Diode. Nobody needs them anyway
* use a heat pad instead of heat paste.

And if you ever plan a redesign, then please:
* Add a capacitor to GND at the RESET input, for some switch-on delay
* Please wire the board so, that the Enable will be pulled high, when the optocoupler is driving! Which means connecting the collector to 5V and the enable to the emitter with a pulldown resistor (the internal Pulldown will be far too big for this).
* add the possibility to drive the 5V supply externally and get rid of the LM317.

And a nice to have would be (although it would increase the cost a little bit, but not much):
* Use also a 6N137 for the dir-signal
* add a transil-diode on the power. This makes sure, the IC can never be damaged due to overvoltage, if the power supply is disconnected and the motor get's manually rotated.


And for a really good drive (although this mod would cost a little, but still not excessive):
* Add a P-Fet which switches the power on, only after some delay and also switched it off before the 5V. But this shouldn't be a big problem, if you generate the 5V out of the input power. So then, you can, as you now do use a lm317 for 5V power generation.

So you see:
* You can already improve them a lot without any additional cost.
* You can improve them much, with only minor additional costs.
* You can make them good, with only small additional costs.