Question: who makes the decisions about what to produce in a market economy?
Answer: capital and financial markets

A market economy is an economic system where decisions regarding investment, production, and distribution are based on the interplay of supply and demand, which determines the prices of goods and services. The major defining characteristic of a market economy is that investment decisions, or the allocation of producer good, are primarily made through capital and financial markets.  This is contrasted with a planned economy, where investment and production decisions are embodied in an integrated plan of production established by a state or other organizational body that controls the factors of production.