Formality and the Holy Sacrifice of the Mass

It's the time of year for "Big" Masses: weddings, professions, ordinations, First Communions, anniversaries.
That means it's also the time of year for The Planning Meetings.
(Incidentally, the prayer cards as gifts was an inspired idea, it has changed the whole tenor of the wedding Liturgy planning sessions, it so kindly, and so up-frontedly makes the points that what we are planning, and what the music should be chosen to enhance is, at its core, a kind of PRAYER. But I digress...)
I had an oft-repeated situation. The people "whose" Mass it was -- oh, there's this wonderful, lively song we used to use for communion at the school where we met... but I guess it's not solemn enough for a wedding.
Now I don't know whether it was or not, whether the actual words and tune could be rendered in such a way as to meet their expectations-- maybe it would have been fine, I don't know what the song in question was.
But I am struck, as so often, by how almost universal is that unexamined assumption that my wedding, my Mass as a matter of course requires a certain degree of formality, that this is something of such importance that the need for solemnity is a given; but at "regular" Liturgies.... eh, whaddevah.
What is the mindset that allows one to feel that ones wedding is a more solemn/important occasion than, oh, I don't know, the unbloody re-presentation of the ritual murder of the Son of God as a sacrifice for ones sins and His giving His very self to one in communion?

I suspect this will always puzzle me.