Why can customize css abbreviation instead of html:5 in snippets.json?

My .vimrc setting on snippest.json.

let g:user_emmet_settings = webapi#json#decode(join(readfile(expand('~/.vim/snippets.json')), "\n"))
let g:emmet_html5 = 1

The ani abbreviation setting in my .vim/snippets.json.

      "ani": "animation:|;",

The ani in css file can expand as animation,snippets.json can take effect.
I expect html:5 expand as following:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title></title>
    <link rel="stylesheet" href="">
</head>
<body>

</body>
</html>

Revise doc defination in my snippets.json as below:

"doc": "html>(head>(meta[charset=${charset}]+title+link))+body",

Why html:5 still expand as below?

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <title></title>
</head>
<body>

</body>
</html>

Why abbreviation setting for html:5 in snippets.json can't take effect ?

mattn / emmet-vim

Why can customize css abbreviation instead of html:5 in snippets.json? #417