wget, by default, saves the fetched web page in a file whose name corresponds to the document at the end of the URL (it does not send it to its standard output). If that file already exists, it adds a number to the end of the name.
If you don't want to save the document, then specify that you'd like to save it in
wget -O /dev/null 'https://domain.tld/index.php?page=cron' >/dev/null 2>&1
wget --output-document=/dev/null --quiet 'https://domain.tld/index.php?page=cron'
It's also a good idea to quote the URL as URLs sometimes contain characters that may be interpreted a filename globbing character or command terminators by the shell (like