Why is housing or other typologies of the middle to lower class so underrepresented in academic discussion concerning pre-modern architecture?
While monumental architecture has definitely not gone extinct in the modern era, considering all the operas, philharmonic halls, museums and other buildings representing the vast array of modern or postmodern styles, it's interesting to notice how the era since Art Nouveau has also been largely represented by housing in academic discourse.
In other words, there are lots of examples of villas, single family houses or apartment buildings that are treated as remarkable and unique examples of architecture, whereas in the eras before modernity housing is kind of overlooked as a set of local vernacular traditions overshadowed by the "great styles" of the time.
As an example, the work of Atelier 66 (Dimitris and Suzanna Antonakakis) has played a major role in projecting some values of vernacular Greek housing reinvented for a modern resident's needs. Yet while they are discussed a lot in academic discourse regarding critical regionalism, like in Kenneth Frampton's work, the Greek architecture that influenced their work is largely overshadowed by monumental works of the Byzantine, Ottoman and Neo-Classical era.
My assumptions of why this happens would be the following:
Modern architecture represents the middle to lower classes far more than pre-modern architecture did. That is expressed as an augmentation of the architectural quality of housing, representing the modern human's ever-increasing needs. Consequently, it is more probable today to see unique and architecturally remarkable housing or workplace projects, such as Le Corbusier's Unités or Rogers's Lloyd's Building, which end up being declared protected as cultural heritage within decades of their construction.
Survivorship bias. Housing has always been considered replaceable and bound to the needs of its era. That is much unlike great monuments, where there is little utilitarian consideration but a strong metaphysical value. This is why monuments like Karnak or Angkor Wat were left behind in a deserted or heavily rebuilt context following the complete disappearance of the metropoles that used to surround them.