I think it's because it sounds lame. Not a lot of people know much about pelicans and just associate them with any other type of bird.
To me the lamest names in professional North American sports are:
Vegas Golden Knights (I just have no idea how they arrived at this)
Anaheim Ducks (at least Mighty Ducks was unique, when they removed that it was just bizarre)
Toronto Raptors (this one is just absurd, making a name out of a movie from a couple years before)
Brooklyn Nets (could not get more bland than this)
Utah Jazz (I kind of like Jazz as a name, but not in Utah)
Washington Wizards (it sounds generic but also doesn't make sense to the place in any way)
And then a bunch of them just sound too generic:
Chicago Bears
Detroit Lions
Carolina Panthers
Atlanta Falcons
Philadelphia Eagles
Atlanta Hawks
Golden State Warriors
Florida Panthers
Arizona Coyotes
Detroit Tigers