From the article:

The “minim” is a short vertical stroke used in handwriting.

In Gothic scripts, many letters — such as m, n, and u — were made up of minims joined by fine connecting strokes. As a result, words like minimum could appear as a confusing row of nearly identical vertical lines (see below).

To improve readability, Middle English scribes sometimes replaced u with o when it preceded m, n, or v, since the rounded o was much easier to distinguish.

This reader-friendly but phonetically misleading convention survives in modern English, which is why words such as come, some, monk, honey, and love are spelled with an o, despite their pronunciations.