I hope my befuddlement is self explanatory and obvious. In Modern English and French, degrade and degrader still negatively connote debasing or demeaning. But academic degrees, goals, and progress are associated with "up" and "above", not "down" or "de-". Why did Old French prefix de- to gradus, not sup-?
c. 1200, "a step, a stair," also "a position in a hierarchy," and "a stage of progress, a single movement toward an end," from Old French degré (12c.) "a step (of a stair), pace, degree (of relationship), academic degree; rank, status, position," which is said to be from Vulgar Latin *degradus "a step," from Latin de- "down" (see de-) + gradus "a step; a step climbed;" figuratively "a step toward something, a degree of something rising by stages" (from PIE root *ghredh- "to walk, go").
Etymologically, degree means ‘step down’, a sense revealed more clearly in its relative degrade . It comes via Old French degre from Vulgar Latin *dēgradus, a compound noun formed from the prefix dē- ‘down’ and gradus ‘step’ (source of English gradual and a wide range of other words). The word’s modern meanings, such as ‘academic rank’ and ‘unit of temperature’, come from an underlying abstract notion of a hierarchy of steps or ranks. Degrade represents a parallel but distinct formation, originally coined as ecclesiastical Latin dēgradāre and passed into English via Old French degrader.
Word Origins (2005 2e) by John Ayto, p 155 Right column.