Unable to map ctrl-l

My _vimrc contains the following lines:

set nocompatible
source $VIMRUNTIME/vimrc_example.vim
source $VIMRUNTIME/mswin.vim
behave mswin


nmap <c-l> :w<CR>

nmap <c-m> :w<CR>

I try to map control+l to :w, and control+m is the control group.

I open a new file, press ctrl-m, the file saves. I press ctrl-l, the command line shows :update. I press ctrl-shift-l, the file saves.

The figure shows the UI after I press ctrl-l. The cursor was on the previous line.

I run :map , <C-L> is registered, but I can only trigger it with ctrl-shift-l.

Why does the mapping of ctrl-l fail?