Why does Emma say that she will never marry in Jane Austen's Emma?

Though discusses her reasons for never marrying in a couple of placesthroughout
Austen's novel, a neat encapsulation of it occurs inChapter 31, or Chapter XIII of Volume II.
Emma is contemplating thevarious ways that Frank Churchill might propose to her following
hisdeparture from Highbury in response to a summons from the Churchills.The ball has to be
cancelled. Emma is bereft of the pleasant attentionsof the handsome and charming Frank. Most of
all, she is certain he wason the verge of declaring his devotion when Mr. Weston came to the
doorto fetch him back home for a speedy return to the Churchills.

In Chapter
30, Emma's response to Frank's first try at revealing his feelings,