Employees with family (or married) are given marriage leave, paternity leave, maternity leave (default for female employees who's giving birth, of course), childcare leave, family care leave, etc. While for single employees, they're only getting the standard leave which are also enjoyed by employees with family.
With more demanding and energy-draining job, most single employees are expected to sacrifice their time more compared to non-single ones, making them to socialize lesser and making friends to be more difficult. In the long run, this creates unhappiness to employees.
Single employees should be treated equally as employees who have families. They should be given equal number of leave days and better work arrangement. For example: single employees should be given social day leave, heartbroken leave, also family leave (parents and siblings are family too, aren't they?)