Can you imagine if Darcy were so foolish or forgiving as to use his influence to get Wickham a post as bodyguard to the monarch? What Wickham would do in such exalted company -- I imagine he would really get into some high-stakes gambling. It would damage the Darcy reputation almost as much as the elopement with Georgiana might have, if it had become public. No wonder Lizzy would much rather not mention it to her husband.