Strictly speaking, there are some transfers, however they're minuscule compared to EU GDP. The simple fact is that rich California pays for poor Montana, but rich Bavaria doesn't pay for poor Greece, doesn't want to and politically can't be forced to do it. IIRC the volume of transfers necessary to reach equilibrium would be around 8% of GDP.
California doesn’t exactly pay for Montana... they do pay for some federal services for which everyone has voted for. In theory though poor management can cause a state to default on its debt.