Why is there a difference between nosegear retraction directions?
For both main and nose landing gear the main and really only consideration is where they can make space for the gear (there is no standard direction for retracting the main landing gear either; the Tu-154 retracts main gear rearwards into the anti-shock body).

The most common configuration is retracting nose gear forward, because it's easy to make space for it there leaving more space for the cargo hold. I don't think the air pressure during gravity extension plays any role in the decision.

Most older Russian planes were however originally designed with glass nose seating navigator, so they did not have the room there. It was no longer the case with Tu-154 though. So they either had other equipment there or were simply used to making it retract rearward and didn't think about the advantage of changing it.

The most common configuration for main gear is retracting it inward into the wing box, but note that the Tu-154 is exception there as well retracting the main gear into the rather large anti-shock bodies. Because they needed the anti-shock bodies they thought how to use them and there were not that many options.