Picture the market as a slope. High up are the expensive things, the smart shops, the careful packaging and the buyers with money to spend. Low down are the cheap things, the plain packaging and the buyers counting what they have. Downmarket points at the low end of that slope. A thing can sit there, or it can move there, and that is the whole word.
From the word’s history
The supplied source entry gives the word as down- + market. The picture is already in the parts: market names the scale, and down- names which end of it you mean.
這份資料裡的來源條目說，downmarket 就是 down- 加 market。畫面直接寫在組成部分裡：market 給你那條由貴到便宜的線，down- 指出你講的是哪一端。
Wiktionary entries supplied in this packet (source_refs kaikki:3f6f69a190036ae4:1088830291:3418 and :1088833709:1270): 'From down- + market.'
登入就可以看每一支怎麼連回核心畫面。