I am not sure I would include oh-my-zsh as someone's personal zshrc. Moreover I thought OP had made a distinction between bash (10k) and zsh (1k) so I am not sure how o-m-z counts as a bashrc? I will take your word for it but I cant imagine what people put in there bashrc to get to 10k. The entire bash-it repository is 8,588 and over a third of it is bash completions which seems to duplicate the majority of what is already provided by bash-completion. And I am not sure that bash-completion is really "my .bashrc."

  $ cd bash-it
  $ sloccount ./ 
  ...SNIP...
  SLOC    Directory       SLOC-by-Language (Sorted)
  3198    completion      sh=3198
  3168    plugins         sh=3168
  1081    themes          sh=1081
  748     lib             sh=748
  242     aliases         sh=242
  135     top_dir         sh=135
  16      template        sh=16
  0       custom          (none)


  Totals grouped by language (dominant language first):
  sh:            8588 (100.00%)

Are there some big bashrc customizations that I might be overlooking?

edited to reflect distinction between parent and grandparent comment

Sorry, I'm not the parent commenter.