The reason that Dr.Tyson gave for excluding Pluto from the museum exhibit was that He considered Pluto to be an icy body and not a planet
Explanation:
Pluto was categorized as a dwarf planet and it stopped being considered a planet, that is the reason why it could not longer belong to and exhibit along with the milky way planets, In 2006, Pluto, Ceres, Makemake, and Eris were considered icy bodies and then Pluto became part of a different category in space order.