When an item is new, in the news, topical, or fashionable, it is easier to create and stimulate demand, so it is worth producers investing in advertising and marketing to increase demand. Later when the product is not new, or in fashion, there will be lower demand. Profit Mints and coin issuing authorities like to make a profit. They have costs and expenses, and many are expected to be run on businesslike lines. Producing special editions of coins for collectors costs more than churning out millions of ordinary coins for circulation.
Most collectors demand high quality, it costs money to produce it.
High Quality Proof coins, commemoratives, and selected specimens all cost extra ,effort, time and money to produce. This extra cost has to be found from somewhere. They are often struck on special machines, at lower speeds, and with greater care. The coin blanks are often polished before striking. The minted coins will be ejected onto a rubber conveyor belt rather than being allowed to fall into a trough or skip.