That's because nobody's honestly looking for it in modern science.  And that's not necessarily the cause of eclipses  There's a fair bit of theory in Flat Earth due to the lack of resources to actually verify the theory.  Nevertheless, the standard mainstream theory about eclipses and the moon in general is falsified by many different observations.

Due to the shape of the Earth being one of the more straightforward questions, this is not a matter of modern science or NASA fraud. A lot of people that are arguably much brighter than us have pondered about this long before. It's safe to assume that from about 300 BC to 1800+ AD every educated scholar believed that the world is a globe.

So you choose to still firmly believe in this idea even if large parts of it are theory, and other parts are refuted by observations? Last time I checked, the Globe Earth model can refute all objections that have been brought up against it, while Flat Earth can't. Just one objection that can be refuted or rather, one assertion that can be disproven, falsifies the complete theory.

What falsifies the standard mainstream assertions about eclipses? And about lunar eclipses? And about the Moon?

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Aristotle (384–322 BC) was Plato's prize student and "the mind of the school".^[49] Aristotle observed "there are stars seen in Egypt and [...] Cyprus which are not seen in the northerly regions". Since this could only happen on a curved surface, he too believed Earth was a sphere "of no great size, for otherwise the effect of so slight a change of place would not be quickly apparent". (De caelo, 298a2–10)

Aristotle was a smart guy. The changing night sky depending on position was apparent to him, but not apparent to some people today.

Perhaps you just want to have a look at the table of contents of the Spherical Earth Wikipedia article and pick some points that are of special interest to you or that you think are easy to refute?

https://en.wikipedia.org/wiki/Spherical_Earth

The section on St. Bede is also quite interesting, given we discussed this matter previously:

Bede the Venerable
The monk Bede (c. 672–735) wrote in his influential treatise on computus, The Reckoning of Time, that Earth was round. He explained the unequal length of daylight from "the roundness of the Earth, for not without reason is it called 'the orb of the world' on the pages of Holy Scripture and of ordinary literature. It is, in fact, set like a sphere in the middle of the whole universe." (De temporum ratione, 32). The large number of surviving manuscripts of The Reckoning of Time, copied to meet the Carolingian requirement that all priests should study the computus, indicates that many, if not most, priests were exposed to the idea of the sphericity of Earth.^[77] Ælfric of Eynsham paraphrased Bede into Old English, saying, "Now the Earth's roundness and the Sun's orbit constitute the obstacle to the day's being equally long in every land."^[78]
Bede was lucid about Earth's sphericity, writing "We call the earth a globe, not as if the shape of a sphere were expressed in the diversity of plains and mountains, but because, if all things are included in the outline, the earth's circuмference will represent the figure of a perfect globe... For truly it is an orb placed in the centre of the universe; in its width it is like a circle, and not circular like a shield but rather like a ball, and it extends from its centre with perfect roundness on all sides."^[79]