Why logrotate using "size" threshold for some log files even though no "size" parameter used in the configuration file?

Issue

• Why logrotate using "size" threshold for some log files even though no "size" parameter used in the configuration file?

• The logrotate config file has no "size" parameter.

  $ cat /etc/logrotate.d/syslog
  /var/log/cron
  /var/log/maillog
  /var/log/messages
  /var/log/secure
  /var/log/spooler
  {
      missingok
      sharedscripts
      postrotate
          /usr/bin/systemctl kill -s HUP rsyslog.service >/dev/null 2>&1 || true
      endscript
  }
  

  But the debug log shows that it is considered to use "size" threshold.

  considering log /var/log/cron
    Now: 2021-03-10 17:45
    Last rotated at 2021-02-25 03:17
    log does not need rotating (log size is below the 'size' threshold)
  considering log /var/log/messages
    Now: 2021-03-10 17:45
    Last rotated at 2021-03-09 03:17
    log does not need rotating (log size is below the 'size' threshold)