The reason: Mesomania requires you to reject the most obvious and clear data on the question of Book of Mormon geography.
If you're still evaluating alternative models of Book of Mormon geography, you might be persuaded by the idea that one model or another will do "whatever the data says."
Here's a Dilbert cartoon that explains what Mesomania scholars and educators really mean when they say "We'll do whatever the data says."
Don't forget that our Mesoamerican friends have already made up their minds--their #1 goal has nothing to do with following the evidence.
Instead, they say, "Our goals are (1) to increase understanding of the Book of Mormon as an ancient Mesoamerican codex." Such a goal is entirely inconsistent with following the evidence.
Beyond that problem, the question is, what data?
The only specific, detailed, and unambiguous declaration about Book of Mormon geography that I know of is Letter VII. Oliver Cowdery, with Joseph's assistance and subsequent endorsement multiple times, made three major points.
1. The final battles of the Nephites and the Jaredites took place in the mile-wide valley west of the Hill Cumorah in New York.
2. Mormon put all of the original records in the repository in the New York Hill Cumorah.
3. Mormon gave his son Moroni only his (Mormon's) abridgment of the original records.
Through Letter VII, Joseph and Oliver established that there is one Hill Cumorah, that it is in New York, that Mormon's repository was there, and that Joseph Smith actually translated two separate sets of plates (because Moroni did not have the plates of Nephi to put in his stone box).
Who accepts this data?
Only those who accept the New York Cumorah.
IOW, proponents of Baja, Panama, Chile, Mesoamerica, Eritrea, Sri Lanka, and everywhere else don't accept this data.
How is this possible, you wonder?
Easy. They don't consider Letter VII "data" because it was just the work of Joseph and Oliver, two men whom, they insist, never had a revelation about Cumorah. Instead, they claim Joseph and Oliver were ignorant speculators who misled the Church about the New York Cumorah.
Those of us who accept Joseph and Oliver note that these two men had personal experience inside Mormon's repository in the Hill Cumorah in New York. We find it irresponsible to reject their unambiguous teaching about Cumorah just because, in the eyes of the scholars, the experiences Joseph and Oliver had inside the repository cannot have been real because it contradicts their theories.
Why do the scholars reject this data?
Purely because it contradicts their Mesoamerican and two-Cumorahs theories.
They seek to accomplish their goal of by suppressing and rejecting any data that contradicts it.
This is no way to reach a consensus.