My apologies, I was being a little facetious. Just a little. :)
The size difference was based on my intuition that when I maintained my own .bashrc and .zshrc, I was able to "get away" with fewer total lines in my .zshrc than my .bashrc. I remember my .bashrc being dozens of pages, my .zshrc was only a couple.
Compare that to my fish init file...all it does is set a few paths and aliases and turn off the greeting, because everything else just works out of the box for me.
It's also remarkably fast because I took great effort to optimize the parts that happen the most. Shell is actually pretty fast if you don't fork and exec all the time...
Well, it's about 400 lines total. Roughly 40% of that is PATH handling functions: add_to, append_to, replace_in, remove_from, prefix and unprefix. They're used like:
add_to PATH /usr/sbin
prefix and unprefix are a macro for a bunch of standard replace_in/remove_froms:
...All of which are managed by different package managers (stow, brew, ports).
All that stuff is the part I optimized so that it only uses bash built-ins and never execs. Converting that away from sed/perl shaved about 8 seconds off my startup time (it's now so fast I don't notice it).
The next 20% is interactive stuff. Setting up the prompt, aliases, stty, etc. This is generally more complicated than it technically needs to be because it's cross platform so it'll run on any unix-y thing with no changes.
Then remaining 40% is a big chunk of shell functions that are mostly unused in my day-to-day life, but kept there to jog my memory if I need to do a certain task.
That adds up to 100%, but it's also worth noting that 27% of that is blank lines and comments.
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."
The size difference was based on my intuition that when I maintained my own .bashrc and .zshrc, I was able to "get away" with fewer total lines in my .zshrc than my .bashrc. I remember my .bashrc being dozens of pages, my .zshrc was only a couple.
Compare that to my fish init file...all it does is set a few paths and aliases and turn off the greeting, because everything else just works out of the box for me.