No, it was excluded from the planets because it was a small icy object surrounded by lots of other small icy objects, many of which are of a similar size, most notably Eris. It also didn't clear the neighborhood around its orbit (basically, asserting gravitational dominance in the area), so it couldn't be classified as a planet. Search up the former planet Ceres to see a similar situation happen with a different planet.
Being too small is too simple of an answer to be scientifically correct.
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