An older issues customers have had with the SugarCRM system was its apparent bias towards a business-to-business scheme. In recent years Sugar has addressed the concern and created ways ease business-to-consumer users into the CRM. A single configuration variable will affect several aspects of the system.
$sugar_config['require_accounts'] = false;
Adding this line to config.php (or preferably, config_override.php) will ensure that creating or modifying Cases will not require the user to select an Account.
Why and How?
Have a look at include\SugarObjects\VardefManager.php for the method applyGlobalAccountRequirements. This function will take any vardef called account_name in certain key modules and make it required, despite module-specific vardef definitions (i.e. in modules/Cases/vardefs.php or custom/modules/Cases/Ext/Vardefs/vardefs.ext.php).
The Case bean itself reverses the requirement if the require_accounts configuration parameter is set.