Interestingly it finds other files files down this path:

select mdfind.path from mdfind where mdfind.query = "kMDItemTextContent == '*o*'" and mdfind.path like '/Library/Application Support/M%';
+---------------------------------------------------------------------------+
| path                                                                      |
+---------------------------------------------------------------------------+
| /Library/Application Support/Malwarebytes/MBAM/Logs/FrontendAgent-501.log |
| /Library/Application Support/Malwarebytes/MBAM/Logs/SettingsDaemon.log    |
+---------------------------------------------------------------------------+

and I see the same behavior across 50+ Mac laptops so seems consistently not indexing those files.