Why does Pope not apply his definition of "Wit" from An Essay on Criticism to his poem The Rape of the Lock?In An Essay on Criticism, Alexander...

In An Essay on Criticism Pope uses "Wit" in two ways. In some instances, "Wit" means the poet writer: "Great Wits sometimes may gloriously offend, / And rise to Faults true Criticks dare not mend;". In some other instances "Wit" means intelligence or skill: "Pleas'd with a Work where nothing's just or fit; / One glaring Chaos and wild Heap of Wit;" "So Schismatics the plain Believers quit, / And are but damn'd for having too much Wit."

In your reference to "the definition of "Wit"," I believe you must be referring to this passage:

Some to Conceit alone their Taste confine,
And glitt'ring Thoughts struck out at ev'ry Line;
Pleas'd with a Work where nothing's just or fit;
One glaring Chaos and wild Heap of Wit;
Poets like Painters, thus, unskill'd to trace
The naked Nature and the living Grace,
With Gold and Jewels cover ev'ry Part,
And hide with Ornaments their Want of Art.
True Wit is Nature to Advantage drest,
What oft was Thought, but ne'er so well Exprest,
Something, whose Truth convinc'd at Sight we find,
That gives us back the Image of our Mind:
As Shades more sweetly recommend the Light,
So modest Plainness sets off sprightly Wit:
For Works may have more Wit than does 'em good,
As Bodies perish through Excess of Blood.

You'll notice Pope uses very many qualifying words such as alone, confine, every, nothing, glaring, wild. He refers to the poet to whom these qualifiers apply as "unskilled." He says this class of poet covers nature with "Gold and Jewels" over "ev'ry Part" because unable to show the "living Grace" of nature. This is a description of a poet who produces false poetry and Pope identifies it as full of extremes and extreme use of "Ornaments," what we call literary devices such as metaphor. It in necessary to note that in no wise does Pope disparage using literary devices, though he makes it quite clear he abhors the extreme overuse of literary devices to try to hide a lack of a poet's wit.

This answers your question then. While excessive use of literary devices, like metaphor and irony, is a mere cover-up for lack of intelligence and poetic skill, Pope admires the just and fitting use of literary devices such as the Greeks and Renaissance poet Wits gave such brilliant example of.

Therefore, in The Rape of the Lock, Pope was following in the "Rules" gleaned from his great predecessors and was most certainly not violating Wit through the witless excess of pointless "Ornaments" of literary devices as he described in the passage above.