(Modulo d'oh because of the industrial revolution and the relatively easy wealth extraction that that enabled;) because the British public had internalized (I would venture to this day) the distinction between upstairs and downstairs and did not present a revolutionary risk to the elite. This then allowed the wise decision of the elite to permit social mobility to those who would work to further the broader cause of the Empire, in all domains including sciences. This is likely a very goldilock moment for any civilization: higher valuation of reason over dogma; a techological and economic production jump that enabled a categorical raising of one nation over many others; a mass population that did not think less of its 'betters' because they were slothful extravagents (as long as they 'acted' superior); and finally the creation of a productive and resourceful middle class that was satisfied to help in the administration and operation of an enterprise that was deemed a national cause: the empire.