You say that like it’s stopped. Have you ever heard this song or this one or this or this, this this or this? Those are all from the past 5-10 years… And if you ever get a chance to listen to “Like Tiny Swords” by Forgotten Cassettes, which is apparently either too new or two unpopular to have their lyics up anywhere, you’ll hear that sort-of-but-not-really-sensical songs are still going strong. 
Good call. That kind of dreck cements Billy Corgan’s place as the most overdramatic, pretentious, unintentionally funny singer of his time.
Que?
Hehe, here’s a webpage that’s got a midi version “Joy to the World” playing.
It was a mondegreen for the hymn “Gladly the cross I’d bear”.
Apparently there is a traditional hymn entitled “Gladly the cross I’d bear”.
It has nothing to do with ursines with misaligned visual organs.
TDN originally took a pass on the song but later realized that they needed a track - either to fill out the minimum number of tracks on an album or the B side of a single, I don’t remember. Anyway, they went ahead and recorded Hoyt’s little ditty then left the country prior to release, probably a tour of some sort. When they returned, they discovered that the song - which they thought would go nowhere - turned out to be a huge hit.
Gliddy, glup, gloopy
Nibby nabby noopy
La, la, la, lo, lo
Sabba sibby sabba
Nooby abba nabba
Le, le, lo, lo
Tooby ooby walla
Nooby abba nabba
Early morning singing song
I have nothing to add to the “Jerimiah was a bullfrog” question, but I will note that Mary Travis (“Mary” of Peter, Paul, and Mary) looks more and more like her “Big Blue Frog” every year…