Why does vim format nginx.conf strangely?

Question

vim

Before gg=G

After gg=G, type format the file.

.vimrc is empty

Answer 1

:help =

={motion}        Filter {motion} lines through the external program
                         given with the 'equalprg' option.  When the 'equalprg'
                         option is empty (this is the default), use the
                         internal formatting function C-indenting and
                         'lisp'.  But when 'indentexpr' is not empty, it will
                         be used instead indent-expression.  When Vim was
                         compiled without internal formatting then the "indent"
                         program is used as a last resort.