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Thank you for your question. Researchers in both California and Oregon have been conducting extensive research on Azadirachtin (Neem Oil) and its impact on pollinator populations. Although the 'old' thinking was that it had to be ingested before it could cause harm, it appears that it may not be as benign as first believed. (http://ipm.ucanr.edu/PDF/PMG/pnw591.pdf) It is, of course, toxic to bees and other insects if it 'lands' on them and smothers them.  Spraying on combs caused full to partial mortality (https://www.tandfonline.com/doi/abs/10.1080/00218839.2016.1260239?scroll=top&needAccess=true&...)  (https://academic.oup.com/jinsectscience/article/15/1/137/2583443)

Since most farmers don't read this, they may not know. But I have experienced that there is confusion about adding adherents to neem oil, frustration that it washes off so fast and is of short-lasting effect, and these may account for farmers using the 'tried and true' commercial insecticides, rather than Azadirachtin.  Hope this is helpful.