@okie,
That's an interest question, okie.
Here, they don't. But many employers do. Nowadays.
Historically, it's part of a deduction from salary/wage for a special purpose.
As there are as well vacancies, bonuses, holiday pay, Christmas bonus, sickness pay, paid further training and education, cheap meals in cafeteria, reduced costs for housing, subsidies for travel costs ... which are tried to be reduced by employers everywhere.
Just social security, health insurance and similar are 28% in Germany (31% average in the EU). [You have to add to this sum vacancies etc.]