The Morgul Way

[easterlinge]

The army Faramir ambushed was heading for the Morannon and thence to Udun. Why didn't they enter Mordor via the Morgul Pass and by the Morgai?

The infrastructure is there, a pass leading to a bridge crossing the Morgai......

I seem to get the sense that the Nazgul Lord's Morgul army was his own privately run force. The Morgul Orc gear was described as being better made than that of Lugburz.

[Wayfarer]

I can answer your first question.

the terrain outside of mordor was much easier to traverse than the gorgoroth. Given the choice between crossing a wasteland, or traveling through a forest and over a plain, they chose the latter.

Also, the morannon opened directly into udun.