Why are archaeologists scared to death of sweet little glacial erratics?

I have been reading a 2018 Aberdeen doctoral thesis by Martha Johnson on the rocks of the Ness of Brodgar -- and also looking at a video which is tied in to the archaeological investigations on the site:

https://abdn.primo.exlibrisgroup.com/discovery/delivery/44ABE_INST:44ABE_VU1/12153047130005941

https://www.youtube.com/watch?v=OwTs-QVvB7U

She has spent a great deal of time and effort in examining the "foreign rock" boulders, slabs, pebbles and artefacts in and around the sites of the archaeological investigations, and purports to be seeking to understand why these stones were used, and where they came from. So far, so good. But in spite of the fact that she mentions the presence of glacial till and has a few mentions of the glaciation of Orkney, nowhere does she discuss ice movement across Orkney or explain that the great bulk of the stones examined are glacial erratics.  She simply slides over the issue of how the stones got to the site,  simply assuming that they were sourced, collected or gathered from specially selected sites by the people who inhabited the Ness.   She says the foreign rocks were "transported to and utilized within the site"...........   and statements like this are scattered throughout the text.  In one place she states that well rounded pebbles found in the digs were collected from nearby beaches -- apparently oblivious to the fact that glacial deposits frequently contain old beach pebbles incorporated into the glacier bed during glacial episodes.

This is quite extraordinary, coming as it is from someone who now holds a doctorate.  I suppose that archaeology in Aberdeen is afflicted by Post-Processualism and claims to go beyond boring things like evidence collecting  into the realms of  behavioural science and psychology -- but to completely ignore the natural processes that might have carried most, if not all, of the foreign stones to the site smacks of carelessness and one-track thinking -- and that is about as polite as I can get.

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Thesis Abstract

This research introduced a geological perspective into an archaeological setting,
the Ness of Brodgar, a Middle to Late Neolithic site in the West Mainland of
Orkney. Discovered in 2003, the site is located on an isthmus of land between
two lochs and is equidistant between the Ring of Brodgar and the Stones of
Stenness stone circles. The site consists of more than two dozen drystone
buildings encircled by a massive wall. To date, ten per cent of the site has been
excavated.
This research established a systematic framework of protocols and procedures for
the recovery, macro geological assessment and identification of the rock and
mineral species in the non-tool, non-structural rocks, termed Foreign Stone for
this research. Once identified, the frequency and distribution of the rock in the
Foreign Stone finds were calculated, providing a geological basis for
understanding any patterns of rock choice across the site. Integrated into a more
conventional archaeological study of the Worked Stone artefacts was a
systematic macro petrological analysis of these finds. Additionally, selected
segments of the interior drystone walling were assessed to identify the rock in the
various members. These petrologic analyses combined to provide insight into the
range of rocks transported to and utilized within the site. Comparative analysis of
the data from all three aspects, Foreign Stone, Worked Stone and Walling, was
undertaken to identify trends in frequencies and patterns of use of the various
rock species. Archival and more current information on the petrologic resources
available within Orkney were synthesized in a gazetteer identifying the location(s)
of rock outcrops and deposits. This permitted the source location(s) of many of
the rocks from the Ness of Brodgar to be identified.

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Ironically, there is another YouTube video on the glaciation of Orkney, presented by Dr Adrian Hall and Dr John Brown -- in which there is a clear description of the glacial deposits, ice movement directions and glacial landforms of the islands.  Martha Johnson does list till occurrences in her thesis, and cites Peach and Horne -- but apparently sees no connection at all between her work and that of geomorphologists and geologists. Weird.

https://youtu.be/3VHbgP4HWNY?si=klGt8lBQ-WmY2YiQ

Reference:
Peach, B. N. and Horne, J. (1880) ‘The Glaciation of the Orkney Islands’,
Quarterly Journal of the Geological, 36(1-4), pp. 648-663

An extract from one of the Peach and Horne maps.

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This all brings into mind the obsessive refusal to talk about, or even mention, glacial erratics and erratic transport in all the articles about West Wales and the bluestones written by Parker Pearson, Bevins, Ixer, Pearce et al.  They do occasionally mention till, but whenever they talk about monoliths, they fail to mention that the whole landscape of Preseli is littered with glacial erratics -- some very local and some far-travelled.  They simply assume that these erratics and the associated  ice movement directions are of no relevance whatsoever to their studies, and talk instead of stones being "chosen", "selected", "fetched", "sourced" or "quarried" from the spots which they see as provenance locations. 

This is of course completely unscientific and even bizarre.  So why are grown men so frightened by an assortment of rather innocuous and innocent pebbles and boulders which surely deserve to be taken into consideration, like all other sweet little stones? Answers on a postcard please.......