It's not just motivation that matters, its representation.
So, we say, "you can't kill an orc because it's an orc" (the grosses oversimplification you can make). We'll accept that at bare minimum.
You place a group of orcs as the villains of your adventure. They are raiders coming from the mountains who are lashing out at the farmlands because they want to feast on the bread and hogs the farmers produce, steal thier treasures and tools, and sacrifice the farmers to thier depraved god of battle and slaughter (those who aren't kept at slaves or breeding stock that is, those half-orc adventures need an origin...)
Classic fantasy right, but also the very excuses that has been used to justify genocide, racism, and other forms of oppression.
So, we say, "Ok these orcs are bad for whatever reason, but not ALL orcs are!" There are good orcs and bad orcs, and not orcs are like this. We remove the "CE" alignment off the generic orc statblock, remove the alignment section out of the orc race. Maybe we move Gruumsh from "God of Orcs" to "God of Slaughter" and make him worshipped by all manner of sentient beings from elves to ogres. Mission accomplished, pop the elven wine, right?
... Where are those good orcs?
Where are peaceful orc tribes? The orcs who have settled and built towns and villages? The orc blacksmiths, guards and scholars living in working the major cities? The orc merchants who hire adventurers to guard their caravans against halfling bandits and raiders? The orc high priests and archmages? The orc nobles and royalty?
It doesn't do any good to say "orcs CAN be any alignment" but continue to use classic "raiders and pillagers" trope because that is an easy motivation that allows PCs to put the orcs to the sword.
Let's take another example, maybe those orc raiders were driven out of thier ancestral homelands by human settlers who turned their sacred lands into farms. Hiding in the mountains with little resources and on the verge of starvation, the orcs mount an attack to claim their ancient homeland back as well as claim reciprocity for the theft and murder of thier ancestors. Except the townsfolk, fearing the orcs who they were told were savage raiders by thier elders to justify the taking of their lands, hire the PCs to go and stop the orcs from lashing out at thier farmlands...
Still ready to slay orcs and take thier pie?
As D&D approaches a more nuanced perspective, the rationale of their actions because harder and harder to justify. Is the Keep on the Borderlands the last bastion of order against the forces of Evil and Chaos that seek to snuff it out, or is it the tip of the spear from conquering forces who seek to reap the riches of marginalized native peoples and ostracized religions? What if it's both?