Wooden walls are something civilians would be able to build, unlike granite walls, and is a fairly straightforward idea they would've been able to come up with on their own, unlike decoy walls. Since wooden walls don't exist anyway, I would assume it's because building them is not simply labor-intensive, but is altogether impractical, for some reason. No idea why that would be, though. Prevalence of weird supernaturally strong chakra trees civilians can't take down?
All of this has to be balanced against perceived cost/benefit, force of habit, culture and traditions, etc. In any case, walls and defensive structure produce nothing of value to the average farmer unless they have foresight and experience to see the value.
I'll admit I misremembered that:
Still, MEW walls sound like "tough walls", not "virtually indestructible walls", so I would assume it applies.
Neither do decoy walls.
Can we agree that 'decoy walls', 'MEW walls' all have varying level of protections balanced against costs?
Tsunade is a great woman and she has lot of experience, but she isn't an end-all be all authority on how to uplift civilians. We should test things out, and see what works, and use our own experience and analysis to determine what's the best way of doing thing.
Let's do this: We'll deploy decoy walls for the majority of villages, explaining to them it might help and
strongly suggest that they should really do it.
And identify all the villages that probably need stronger walls, either palisade(in which case, we help chop woods), or MEW if it's necessary. Villages that have bigger populations have bigger values, and thus warrant more protection.
If we think, based on evidence, that more villages need better walls, then we adjust our strategy.