We are talking a pernicious and nasty, well organized fungus here.
Given the concentration of wealthy/influential types, and the means by which the fungus exerts control (It engages in symbiosis with what effectively are 1%ers in terms of wealth or power, rather than turning them into reproductive bodies) and thus avoids being directly confronted (the leaders perceive no threat to themselves, despite still being subtly and profoundly influenced biochemically, and statistically they already cared less than 2 shits about the under classes anyway, coupled with the psychotropic effects of infection in the lower classes inducing child-like states of "social harmony" and "Contentedness" with their lots in life, which is a "good" change from being unhappy and demanding concessions) it makes sense that such a place would have a high percentage of symbiotes vs reproductive forms.
Consider:
Much like a colony of bees segregates morphologically into societal roles, without strife or rebellion (for the most part), the fungus also segregates the population based on social dynamic castes, and makes these determinations through a complex and dizzyingly sophisticated network of biochemical interactions with the host to determine if it will induce fruiting, or if it will simply mindcontrol the subject and increase their physical/mental abilities instead. Rather than develop biological defenses against attack like poison or thorns, it has instead refined its infection strategy to effectively eliminate all sources of competition or predation. It does this by forcibly realigning its infected demographic into a truly integrated societal heirarchy, through biochemical manipulation of the behaviors and thoughts of all members of the society. The fungus is not itself capable of complex, or rational thought-- rather, it achieves evolutionary fitness through coopting the intelligent action of its vector to further its rate of infection, and to sustain infected colonies.
To facilitate that goal, it produces reproductive/worker class morphologies, protector class morphologies (Our plumbers fall into this category), and social heirarch class morphologies. (Princess peach, rich fatcats on wallstreet, et al.) The fungus does not halt advancement of an infected society, instead it redirects it in ways that benefit the continued presence of the fungus, including mind control of all subjects at all levels. Worker/reproductive forms are child-like and naive in their devotion to the societal order and their leaders. Protectors feel morally compelled to protect the paradigm that emerges after infection from all outside threats and have enhanced physical properties, and the heirarch classes are subtly bent away from shameless self-indulgence and indolence into being more careful planners and caretakers of the social system (thus assuring that the worker class gets everything it needs (and thus, assures that the fruiting bodies they host are properly nourished, and that they travel well, spreading their spores in wider areas, etc) and have improved cognitive faculties to accommodate this.