Why does ClamD's SystemD service fail to invoke by default?

By default, systemctl status clamd@scan returns:

× clamd@scan.service - clamd scanner (scan) daemon
     Loaded: loaded (/usr/lib/systemd/system/clamd@.service; enabled; preset: disabled)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: failed (Result: exit-code) since Fri 2026-05-08 11:04:42 BST; 59min ago
 Invocation: 2c9d0cfdafc3466f86ca80f6615c2a50
       Docs: man:clamd(8)
             man:clamd.conf(5)
             https://www.clamav.net/documents/
    Process: 1593 ExecStart=/usr/sbin/clamd -c /etc/clamd.d/scan.conf (code=exited, status=1/FAILURE)
   Mem peak: 2.3M
        CPU: 5ms

May 08 11:04:42 Beedell.RokeJulianLockhart.desktop.SSV2AY systemd[1]: clamd@scan.service: Scheduled restart job, restart counter is at 5.
May 08 11:04:42 Beedell.RokeJulianLockhart.desktop.SSV2AY systemd[1]: clamd@scan.service: Start request repeated too quickly.
May 08 11:04:42 Beedell.RokeJulianLockhart.desktop.SSV2AY systemd[1]: clamd@scan.service: Failed with result 'exit-code'.
May 08 11:04:42 Beedell.RokeJulianLockhart.desktop.SSV2AY systemd[1]: Failed to start clamd@scan.service - clamd scanner (scan) daemon.

However, after uncommenting two values of its default configuration, per:

That is actually relevant:

I’d copy it into Discourse, but can’t. If you can’t access it, see:

…it operates:

● clamd@scan.service - clamd scanner (scan) daemon
     Loaded: loaded (/usr/lib/systemd/system/clamd@.service; enabled; preset: disabled)
    Drop-In: /usr/lib/systemd/system/service.d
             └─10-timeout-abort.conf
     Active: active (running) since Fri 2026-05-08 12:07:12 BST; 3min 2s ago
 Invocation: f148f5ecb0d94509a6501870f845f967
       Docs: man:clamd(8)
             man:clamd.conf(5)
             https://www.clamav.net/documents/
    Process: 33886 ExecStart=/usr/sbin/clamd -c /etc/clamd.d/scan.conf (code=exited, status=0/SUCCESS)
   Main PID: 33888 (clamd)
      Tasks: 2 (limit: 37276)
     Memory: 950.8M (peak: 1G)
        CPU: 3.818s
     CGroup: /system.slice/system-clamd.slice/clamd@scan.service
             └─33888 /usr/sbin/clamd -c /etc/clamd.d/scan.conf

May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: Mail files support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: OLE2 support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: PDF support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: SWF support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: HTML support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: XMLDOCS support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: HWP3 support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: OneNote support enabled.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY clamd[33888]: Self checking every 600 seconds.
May 08 12:07:12 Beedell.RokeJulianLockhart.desktop.SSV2AY systemd[1]: Started clamd@scan.service - clamd scanner (scan) daemon.

Why is its default configuration inoperative?

I ask because, without vibecoding a solution (what a world we live in!), I wouldn’t have been able to ascertain that those two values, of the hundreds listed, were what I should uncomment. I seriously doubt that anyone should need to become that intimately familiar with the ClamAV service merely to utilise the most basic of AV systems.