Wget Tips – How to Download Files When the Page Makes You Wait

It's because wget is newely invoked for each url. Use the -i option to feed a list of URLs to wget:

$ wget -i urls.txt --wait=30

From the manual:

-i file
--input-file=file

Read URLs from a local or external file. If - is specified as file,
URLs are read from the standard input. (Use ./- to read from a file
literally named -.)  If this function is used, no URLs need be present
on the command line. If there are URLs both on the command line and in
an input file, those on the command lines will be the first ones to be
retrieved. If --force-html is not specified, then file should consist
of a series of URLs, one per line.

However, if you specify --force-html, the document will be regarded as
html. In that case you may have problems with relative links, which
you can solve either by adding "<base href="url">" to the documents or
by specifying --base=url on the command line.

If the file is an external one, the document will be automatically
treated as html if the Content-Type matches text/html. Furthermore,
the file's location will be implicitly used as base href if none was
specified.

You can't do it purely in one invokation of Wget. This stems from the definition of Wget's -O option, which doesn't simply mean name of saved file, but rather is a shell redirection of stdout.

If all the names of the files are different on the server, then you can still do this fairly quickly by downloading all the files in a single invokation of Wget and then using a shell script to rename them.

You're right in that multiple invokations of wget will be slow. The process startup and teardown is one aspect, but needing to make a new HTTP connection to the server for each of the files can add up very quickly