Nginx captured regex can't be reused later for includes?

I capture the server name like this:

server_name ~^(?<account>.+)\.myapp\.io$;

an later i try to use it on the same file, like:

include $account.conf;

but it returns:

nginx: [emerg] open() "/etc/nginx/$account.conf" failed (2: No such file or directory)

of course, the file exists.

If i use it somewhere else, it works, like:

access_log /var/log/nginx/$account-access.log;