Why is the Tract for the first Sunday in Lent so LONG!?

For parishes that use the pre-conciliar Latin Missal, the Ordinariate's Divine Worship Missal, or even the Ordinary Form of Mass with music from the Graduale Romanum, you might have noticed the ridiculously long chant that came before the Gospel reading yesterday for the first Sunday in Lent's Mass. During this season, we've banished the Alleluia and put an extended psalm called the Tract in its place. The very name tractus implies an drawn-out psalm, but in practice, this comes out to only two or three additional verses. For the First Sunday in Lent, though, the complete Psalm 90(91), Qui habitat, is used. The Ordinariate's translation gives it as such:

V. I will say unto the Lord, Thou art my hope and my stronghold: my God, in him will I trust.
V. For he shall deliver thee from the snare of the hunter: and from the noisome pestilence.
V. He shall defend thee under his wings: and thou shalt be safe under his feathers.
V. His faithfulness and truth shall be thy shield and buckler: thou shalt not be afraid for any terror by night.
V. Nor for the arrow that flieth by day; for the pestilence that walketh in darkness: nor for the sickness that destroyeth in the noon-day.
V. A thousand shall fall beside thee, and ten thousand at thy right hand: but it shall not come nigh thee.
V. For he shall give his Angels charge over thee: to keep thee in all thy ways.
V. They shall bear thee in their hands: that thou hurt not thy foot against a stone.
V. Thou shalt go upon the lion and adder: the young lion and the dragon shalt thou tread under thy feet.
V. Because he hath set his love upon me, therefore will I deliver him: I will set him up, because he hath known my Name.
V. He shall call upon me, and I will hear him: yea, I am with him in trouble.
V. I will deliver him, and bring him to honour: with long life will I satisfy him, and show him my salvation.

At my Ordinariate parish yesterday, it was sung to a basic psalm tone. I suspect the vast majority of churches prior to Vatican II did the same. There's only one time I can recall personally singing the full chant melody given in the Liber Usualis--a true marathon of neumes which takes at least 12 minutes to chant. It was oddly not even at a well-established Latin Mass community, but rather for then-new TLM out in the sticks: Ss. Cyril & Methodius in Shiner, Texas. Back in 2011, our schola was invited as a guest choir on a Sunday which just happened to be the beginning of Lent. I'm not sure if that community had any more exposure to Gregorian chant than the Missa de angelis, and yet, we mercilessly brought the full Tract upon them. I even have video evidence of that day below (beginning at the 1:49 mark):

I vaguely recall the priest saying that he didn't have much of a homily prepared because the Tract was a sermon in itself. I've sometimes wondered why, though, this chant is so much longer than virtually all of the others given in the Liber? 

There's the theory that the graduals and tracts of the ancient Church were all supremely long, but the laziness of succeeding generations caused them to be peeled back to mere fragments (as was the case with the Offertory chants)--the Church wished to leave the First Sunday in Lent's tract untouched as a penitential reminder of the fervor of past ages. My friend Mr. DiPippo, editor of the New Liturgical Movement, says that there's no real evidence for this claim being true in the Roman Rite; that it was made up to justify the invention of the responsorial psalm for the post-conciliar rite's lectionary. Perhaps he's right and this is just another one of those myths by "liturgists" that's been repeated so many times that it's been mistaken for truth even by great liturgical scholars. I haven't done the due diligence in my studies to say one way or another.

My favorite explanation for this tract's length is the one given by my pastor in his sermon yesterday. He referenced the Gospel lesson (which, at least this year, is the same for both the old and new lectionaries): Christ's forty-day trial in the wilderness as described in Matthew. Our Lord's retreat into silence and fasting is the very inspiration for Lent, so what could be a more appropriate Gospel for this Sunday? Near the end of the fast, the devil appears and tries to tempt Jesus using Scripture. Specifically, he quotes Psalm 90(91). I quote from the St John Fisher Missale translation, one of my favorites, below, and give my emphases to the psalm quote:

Then the devil took him up into the holy city, and set him upon the pinnacle of the temple, and said to him: "If thou be the Son of God, cast thyself down: for it is written that he hath given his Angels charge over thee, and in their hands shall they bear thee up, lest perhaps thou dash thy foot against a stone." Jesus said to him: "It is written again: Thou shalt not tempt the Lord thy God."

The devil tricks us, my pastor said, by quoting Scripture out of context. To counter this deceit, the Church presents the entire psalm in the liturgy so that we can hear and understand what Satan tried to bend to his own ends in its full form.

Whether or not that explanation can be proven beyond a doubt by historical-critical study, I find it to be a profound spiritual explanation for one of the most gruelingly long chants I've ever had to sing.