In some ways, this is part of a larger phenomenon. Good Friday and Easter are supposed to be the highlights of the Christian calendar. Yet if you measure them by something like specialized music, they are trivial compared to Christmas. Don't believe me? Ask someone who claims Christian roots to name their favorite Christmas carol and they will have major problems narrowing their list down to five examples. Then ask them to name their favorite Easter hymn and it's a rare bird who can think of one. Of course, it doesn't help that most Easter sermons sound remarkably like funeral sermons. And as for Palm Sunday, if it weren't for the fact that my mother would sing an obscure number called Open The Gates of the Temple every year, I couldn't think of any music for the occasion—and church music was a major part of the family business.
All of this is quite unfortunate because Palm Sunday and its lessons form a major elements of how Christianity came to be practiced.
1) According to the legend, Christ rode into Jerusalem on the back of a donkey—NOT a horse like a conquering general. And while Christianity has a long bloodthirsty history, it also has serious wings (Quakers, Mennonites, etc.) devoted to ending wars and abolishing slavery.
2) Christ supposedly ended his triumphant entry by driving the moneychangers out of the temple. When I was a kid, an old farmer solemnly informed me that this is the primary lesson of Christianity. "Christ wanders a tiny area of the world healing the sick, making wine for weddings, comforting the oppressed, feeding the hungry, and teaching that the kingdom of God could be in each one of us. Nothing happens. But he starts messing with the moneychangers and they brutally executed him in less than a week on completely trumped-up charges."
And just think, that old farmer had never heard of Lloyd Blankfein or Jamie Dimon.
The Palm Sunday story from Matthew (King James Version)
Matt.21Matthew 21:5 first appeared in Zechariah 9:9.
 And when they drew nigh unto Jerusalem, and were come to Bethphage, unto the mount of Olives, then sent Jesus two disciples,
 Saying unto them, Go into the village over against you, and straightway ye shall find an ass tied, and a colt with her: loose them, and bring them unto me.
 And if any man say ought unto you, ye shall say, The Lord hath need of them; and straightway he will send them.
 All this was done, that it might be fulfilled which was spoken by the prophet, saying,
 Tell ye the daughter of Sion, Behold, thy King cometh unto thee, meek, and sitting upon an ass, and a colt the foal of an ass.
 And the disciples went, and did as Jesus commanded them,
 And brought the ass, and the colt, and put on them their clothes, and they set him thereon.
 And a very great multitude spread their garments in the way; others cut down branches from the trees, and strawed them in the way.
 And the multitudes that went before, and that followed, cried, saying, Hosanna to the Son of David: Blessed is he that cometh in the name of the Lord; Hosanna in the highest.
 And when he was come into Jerusalem, all the city was moved, saying, Who is this?
 And the multitude said, This is Jesus the prophet of Nazareth of Galilee.
 And Jesus went into the temple of God, and cast out all them that sold and bought in the temple, and overthrew the tables of the moneychangers, and the seats of them that sold doves,
 And said unto them, It is written, My house shall be called the house of prayer; but ye have made it a den of thieves.
Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he is just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass.And as G.F. Handel used it in his Messiah.