The ad at left appeared in the Los Angeles Times on September 5, 1969. The shoes of this year — chunky and low-heeled, in colors like "antique brown," olive and navy, were considered sexy. Gwen of Sociological images notes:

It's a great example of how quickly fashion standards can change. Today I'm pretty sure most, if not all, of these shoes would be considered old-fashioned and wouldn't be marketed as sexy. Our ideas of what constitutes a "sexy" woman's shoe today includes a higher, thinner heel, meaning they're also in general less stable, harder to walk in, and worse for your feet than shoes with a chunky heel like these.

All of this is true. But we should also remember that in 1969, skirts were pretty short; these shoes were paired with a lot of leg. Check out this picture of Jane Birkin in 1968, or this "Young New Look" of 1969.