Comment 1 for bug 84104

I interpret the --no-dns-cache man documentation to suggest this behavior is intentional. Here's the relevant excerpt.

--no-dns-cache
Turn off caching of DNS lookups. Normally, Wget remembers the IP addresses it
looked up from DNS so it doesn’t have to repeatedly contact the DNS server for
the same (typically small) set of hosts it retrieves from. This cache exists
in memory only; a new Wget run will contact DNS again.

However, it has been reported that in some situations it is not desirable to
cache host names, even for the duration of a short-running application like
Wget. With this option Wget issues a new DNS lookup (more precisely, a new
call to "gethostbyname" or "getaddrinfo") each time it makes a new connection.

[snip]