There has to be a really good reason beyond a landing platform and a shield generator why the Ewoks would fight the imperials.

What was the motivation of the Indians fighting the US government?

They were taking their land and relocating them or worse.

I think we have to rethink the entire motivation for why the Ewoks would be so aggressively fighting a guerilla war against the empire.

Because in the grand scheme of things a landing platform and shield generator have a small footprint on Endor.

We need something grand. Something more evil the empire is doing on Endor.

And whatever you think of the film Avatar, Cameron gave the humans a good motivation for why they're deforesting and mining Pandora. And also why the Navi are fighting back so fiercely.

It's funny that Cameron used many of the same ideas Lucas had in his earlier drafts of ROTJ. The Earth is all used up. The humans are searching for more areas to exploit and mine. They find the lush world of Pandora and begin despoiling it.

In the earlier drafts of ROTJ, Had Abbaddon was all used up. The imperials are searching for more areas to exploit and resettle people from Had Abaddon. They find the lush world of Endor and begin despoiling it.