Minderwiz
I think that it was a matter of language. Greek and Latin, like English, distinguish between "father" pater and "parent" parens (Lat.) or goneus (Gk); in Arabic, however, walid means both father and parent. If the fourth house is thus the "house of fathers", it seemed natural to look for a "house of mother" and to find it in the seventh house (wife) from the fourth (father). But there is some logic in this, for the tenth is the house of authority and it is the mother who represents the first authority figure in our life. This interpretation lasted in Europe down to the 19th century.
The reversal (mother = 4, father = 10) started in the late 19th century. I presume it was based on the simplistic equation of home (fourth) to the mother, and work (tenth) to the father.
Thanks for the language background, especially the Arabic. That seems to providea goodt rationale of the mother becoming tenth house in later Astrology. As it was Arabic texts that reintroduced Astrology as a worthy area of study, the Arabic link is very important in Western Astrology. I think you are right about the reversal in Modern Astrology, though there's also the supporting idea of Sign=House=Planet andCancer being the fourth sign, feminine and nurturing (at least as viewed from the modern perspective)/ I see a lot of reference to that by the moderns. Oddly they ignore the fact that the tenth sign is Capricorn and it too is a feminine sign (and still viewed as such) but through Saturn it does have associations with labour and toil.