Why does quantum computing need so many qubits if one qubit can be in multiple states?

[KnotKnull]

I thought quantum qubits can be 0 and 1 simultaneously through superposition. So why do we need thousands of qubits to do useful computation? Shouldn't a few qubits be enough?

[TheGame]

Superposition is useful but alone it's not enough. A qubit in superposition can represent 0 and 1 but when you measure it you get one answer. You lose the superposition. That's the measurement problem

[TealBear]

Quantum advantage comes from entanglement not just superposition. Entangled qubits are correlated in ways that have no classical equivalent. To explore large problem spaces you need many entangled qubits working together