This is an unusual song. It's something we all know, from The Wizard of Oz, sung by Judy Garland. But this version was never a hit.
However, it's been featured in numerous commercials. I also remember it was played as Anthony Edward's character, Dr. Green, was dying in the TV medical drama "ER." The song was featured extensively in that episode. So even if it never was heard on Top 40 radio, most of us have been exposed to the Israel Kamakawiwo'ole version. There is a Wikpedia page devoted to it as "Somewhere Over The Rainbow/What A Wonderful World." He did it at 3 a.m. in one take, according to the write up. The song charted as a minor hit in the U.K., Scotland and Ireland, but not in the U.S.
And finally, Kamakawiwo'ole passed away back in 1997. So it's not like he can promote the song today. The only radio station I've heard it played on is KTWV Los Angeles, 94.7 The Wave. It aired during the Smooth Jazz era and continues to rotate these days on The Wave in its Urban AC/Smooth AC format.
WBEB is noted for its extensive research of its playlist. So this song must be testing well, and WBEB is wise enough to test it, even though it has no U.S. chart history.