Why are individual investors called "retail" investors?

As far as I understand it, "retail" refer to big stores that sell to individual consumers and retail investors refers to individuals. Wouldn't it make more sense for a "retail investor" to refer to the big companies that engage in mass trading?

Retail in the sense of buyer and seller of generally small quantities of stocks or bonds, usually on a non-professional basis. Contrast with large (wholesale) investors, who are professionals who buy and sell larger quantities (pension/mutual funds etc.)

Retail investor noun [ C ] FINANCE, STOCK MARKET UK US

a member of the public who makes investments, not a large organization or business that makes investments:

• The Bank is wooing retail investors; it has just published a booklet on the virtues of gilts.

(Cambridge Dictionary)