It's not just supply; you should also consider demand.

Proof used to be extraordinary and very expensive. Franklin mint, Italcambio and the like turned that around about three decades ago by issuing more proofs than uncs. While proof is still desirable in the US, Canada and parts of Asia, it has lost its shine in Europe. For an extreme example, consider the Olympic Games proofs of the Soviet Union. They generally sell at the same price as the uncs. Sets fared even worse. The proof sets of the Franklin mint may sell at a lower price than the unc sets.

I would expect more and more collectors being disinterested in modern proofs and proof sets as it becomes clear to the holdout collectors that proofs have big disadvantages: easy to deteriorate, difficult to sell, grade inflation by the introduction of BU and "prooflike", difficult to photograph. In that sense, the low mintages are a sign of low interest.

Standard disclaimers: if anyone is interested in collecting proof sets that's none of my business. Coins are not a suitable investment.

Peter