Why isn't St Luke portrayed more often in painting?

Here is a page: 1.Saint Luke Painting the Virgin. The image at the bottom of the page is of Vasari as Luke painting the Virgin Mary; the artist assuming the mantle of Luke. Notice the ox next to the artist.

  1. Maarten van Heemskerk paints himself as Luke painting the Virgin Mary, 1532. Notice Saint Luke and his attribute, the ox painted as bas-relief ornamentation on the artist's seat.

St. Luke painting the Virgin Mary by Maarten van Heemskerk, 1538-40.

  1. St. Luke Painting the Madonna by Jan Gossaert (1520-25)

  2. St Luke Painting the Virgin Mary by Marten de Vos, 1602

  3. Saint Luke Painting the Madonna and Child in the Presence of Raphael.

  4. Derick Baegert Saint Luke painting the Virgin Mary, triptych

  5. Saint Luke Painting the Virgin by Theobald Reinhold Freiherr von Oer

  6. Pierre Mignard - St. Luke Painting the Madonna and Child

  7. St Luke Displaying a Painting of the Virgin by Guercino, 1652-53

  8. Francisco de Zurburan, c.1660.

  9. Saint Luke painting the Virgin by Giuseppe Antonio Petrini

  10. Luke the Evangelist , Grandes Heures of Anne of Brittany, Queen consort of France (1477-1514).

  11. St. Luke the Evangelist by Vladimir Borovikovsky.

  12. Lucas van Leyden, etching, Luke the Eveangelist

  13. Saint Luke the Evangelist, icon

  14. Saints Ambrose and Luke by Correggio

Bartolomeo Passerotti - The Coronation of the Virgin with Saints Luke, Dominic, and John

/r/ArtHistory Thread