We can't apply the same treatment to Tenochtitlan or other places for a simple reason: it's a matter of scale. I'm going to use the pixel map, that we use to draw the locations, to show what I'm talking about.
Here is Lake Texcoco, with the island of Tenochtitlan marked in - it's 6 pixels:
View attachment 1304722
This is what happens if I grow it to 100 pixels, the bare minimum threshold that we consider acceptable for a location to be considered playable in the 3D map:
View attachment 1304729
This looks more like modern City of Mexico than Tenochtitlan, as there's no Lake Texcoco anymore, I'd say...
On a personal level, I'd also love to have Tenochtitlan portrayed as an island; but project-wise, this is what we all think will work better for it from both a gameplay and a visual perspective
In Venice, we've been able to make an exception for two reasons: it already had the lagoon around it, allowing us to 'fake' its shape quite decently; and because of it being so important for gameplay reasons, as now it will have the behavior we want for it.
PS: Before anybody asks - we can't share the pixel map with you yet, sorry.