In Europe, why were there few portraits showing a real likeness of the subject before the 15th century?

Question

According to the Wikipedia page on portrait painting in the middle ages, it was not until after 1350 that portraits ‘became clear likenesses’.

This seems to be confirmed, for England at least, by the following text on Richard II

This wooden panel-painting is the earliest known portrait of an English monarch, dating from the 1390s.

Source: https://upload.wikimedia.org/wikipedia/commons/a/a1/Richard_II_King_of_England.jpg

In France, it seems that Charles VI (died 1422) was the first monarch there to have his likeness captured by a contemporary artist, in 1412. It also appears that the large majority of portraits of pre-1400 monarchs such as Henry II of England and Louis VII of France were done during the 17th and 18th centuries.

This is puzzling given that accurate portraiture was common enough in ancient Greece and continued up to the 4th century in Rome (at least). After this,

the interest in an individual likeness declined considerably.

What were the reasons for this decline and why did it take so long for Europeans to become interested in lifelike portraits?

Judging by the exquisite artwork found on early medieval manuscripts, the reason could not have been lack of talent. Granted, this is a different kind of art but there is no reason, I think, why skilled portrait artists could not have flourished had there been a demand for them.

Also, for people (crusaders for example) who were away from their homeland for a long period of time:

Wouldn’t people with sufficient means have wanted and been able to afford visual images of family members and loved ones?

Answer 1

A personal opinion, which I admittedly cannot back with sources atm, but I suspect it had as much to do with the "rise of the individual" during the Renaissance. Writers, artists etc are largely, though not entirely, anonymous before that. The Reformation emphasised personal salvation, an individual relationship with the Divine, and the individual, as opposed to the group, community, caste or class, began to step out of the shadows - cf Hamlet "What a piece of work is a man!" Earlier, the individual was simply not important, so why would s/he be painted?

Answer 2

It was a matter of medieval iconography, which in turn had a religious basis. That is, Christian themes such as God, Christ, and the Madonna, were depicted in standardized, stylized ways. Mere "kings" did not hope for any better.

Also, until the turn of the 15th and 16th centuries, most painters were also wooden "printers." Germany's Albrecht Durer was a case in point. So most painters, of portraits or otherwise, created paintings much like wooden print.

It was the Renaissance, with its emphasis on secular themes stemming from pre-Christian antiquity that broke the above mold. And the widepread adoption of Gutenberg's printing press caused the two arts to diverge, with people choosing one or the other. Concurrent events in art, such as the development of the "third" dimension, and the greater use of color helped artists to make that divergence.