Why was it, in Lydia's imagination, a visit to Brighton would make her very happy?

Lydia's imagination was filled with men, parties, men, attention, men, flirtation, and more men at her back and call.

In Lydia's imagination, a visit to Brighton comprised every possibility of earthly happiness. She saw, with the creative eye of fancy, the streets of that gay bathing-place covered with officers. She saw herself the object of attention, to tens and to scores of them at present unknown. She saw all the glories of the camp--its tents stretched forth in beauteous uniformity of lines, crowded with the young and the gay, and dazzling with scarlet; and, to complete the view, she saw herself seated beneath a tent, tenderly flirting with at least six officers at once.