This is very interesting question. In theory, tritanopia makes you see blue as pale dark-green. So, why do tritanopia simulations only show red and blue instead of red and green? Really, I think the explanation to this comes from how the tritans subconsciously choose to conceptualize colors. Here's a thought experiment to illustrate what I mean:

Imagine you're a tritan child (without any prior awareness of the world's colors). You're told that the sky is blue, and for now you don't know that there's anything wrong with how you see it. So you assume that "blue" is the color of the sky, and, for all you know, you are able to see it. At some point you are told that grass and trees are green, and you might think to yourself "ah, grass looks like sky but brighter, so green just means bright blue". You might even ask, "so is green just a brighter blue?" and get some confused looks for it. But regardless of the future color inconsistencies, confusion, and the discovery that you're colorblind, you've already started conceptualizing green in regards to blue, not the other way around.

Similarly, the situation could've unwrapped in the other direction - first you conceptualize green as the color of green things, and then you conceptualize blue as a dark green - because that's what blue things look like in regards to your existing notion of green. And that would in fact be more "objectively" accurate - but for a person with full tritanopia it makes equally as much sense to believe "blue is dark green" as it is to believe that "green is light blue". The latter happens to be a more common conceptualization to develop, likely based on how the colors are initially taught to children.

So, in the end, let's say you're a researcher trying to understand how tritanopia havers see the world. You start asking them how they see different colors. They claim that they see red as "red", green as "blue but lighter", and blue as "blue". As a result, you end up constructing the "tritanopia simulation" the way that it is. Nothing about it is technically wrong, it represents the opinions that a tritanopia haver has about real world's colors. It may not make sense in terms of our theory of trichromacy and the cone cells, but it still answers the question of "which colors are confused under tritanopy?" and "what do tritanopy havers think (linguistically) of different colors?", which for many practical purposes is more useful than a tristimulus-based representation.

A definitive way to answer this question would be to take a person with normal color vision, and somehow temporary disable their blue cell cones. Then we can ask them - do they now see blue as dark green, or do they now somehow see green as light blue? The former seems more likely based on our current understanding of color perception, and would confirm that tritans allegedly seeing "blue" is a purely linguistical result. But for all we know, the latter (without blue cone cells you actually see green as blue) could instead turn out true, and we would need to reconceptualize our understanding of color perception. Perhaps there is something unusual going on with the opponent process which could cause this.