As a performance analyst I can attest to this.
Before I got the job I am in now, I was stuck in a minefield of unpaid internships. After leaving Uni I was employed by a Premiership team, full time, unpaid (bar expenses). I was happy enough to take the role as I thought I could impress and get a paid position afterwards, or at least get a great reference - but no. After the 12 months is up the Club simply say thank you and goodbye, before bringing in another unpaid intern for the following season.
Afterwards, I spent two years looking for jobs in the field but they were all the same. Unpaid internships. Eventually I found one but I was extremely lucky!
No company should be able to employ someone full time without pay. As someone said earlier, it completely rules out people who can't afford to have no income.