Why do we say "Marry in haste, repent at leisure"?

Meaning:

Get to know somebody very well before you marry them, or you may regret it later.

Background:

The sentiment of this proverb has been traced back to Edmund Tilney's, A briefe and pleasant discourse of duties in mariage, called the flower of friendshippe, published in England in 1566:

This loue must growe by little and little,
and that it may be durable, must by degrées
take roote in the hart. For hasty loue is soone gone.
And some haue loued in post hast,
that afterwards haue repented them

But the first known expression in broadly its modern form is in William Congreve's comedy of manners The Old Batchelour, 1693:

Thus grief still treads upon the heels of pleasure:
Married in haste, we may repent at leisure.

In between these dates, Shakespeare took a stab at the concept in The Taming of the Shrew (1590/1592)

Katharina
No shame but mine: I must, forsooth, be forced
To give my hand opposed against my heart
Unto a mad-brain rudes by full of spleen;
Who woo'd in haste and means to wed at leisure.
I told you, I, he was a frantic fool,
Hiding his bitter jests in blunt behavior:
And, to be noted for a merry man,
He'll woo a thousand, 'point the day of marriage,
Make feasts, invite friends, and proclaim the banns;
Yet never means to wed where he hath woo'd.
Now must the world point at poor Katharina,
And say, 'Lo, there is mad Petruchio's wife,
If it would please him come and marry her!'

And Lord Byron expressed it elegantly in Don Juan (1819-24)

Now hatred is by far the longest pleasure;
Men love in haste, but they detest at leisure.

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