The incentives and knowledge of bureaucrats create another peculiar problem for “rule by experts”.  On the one hand, the bureaucrats that operate the various governmental agencies are necessarily the “experts” on these programs.  Who can be expected to know more than the managers of the myriad administrative fiefdoms?  On the other hand, these specialists are the least likely people to desire limiting these bureaucracies, because they have self-selected to their agency of choice.  Milton Friedman makes this point in his typically understated manner on pages 186-187 of Capitalism and Freedom:

The issues involved become very technical and complex.  The layman is often incompetent to judge them.  Nationalization means that the bulk of the “experts” become employees of the nationalized system, or university people closely linked with it.  Inevitably, they come to favor its expansion, not, I hasten to add, out of narrow self-interest but because they are operating within a framework in which they take for granted governmental administration and are familiar only with its techniques…

Effective control by Congress over the operations of such agencies as the Social Security Administration becomes essentially impossible as a result of the technical character of their task and their near-monopoly of experts.  They become self-governing bodies whose proposals are in the main rubber-stamped by Congress.  The able and ambitious men who make their careers in them are naturally anxious to expand the scope of their agencies and it is exceedingly difficult to prevent them from doing so.  If the expert says yea, who is there competent to say nay?  So we have seen an increasing fraction drawn into the social security system, and now that there remain few possibilities of expansion in that direction, we are seeing a move toward the addition of new programs, such as medical care.