In a parliamentary system, the people vote on a party, rather than a person, and the party decides the individuals who get elected. There's less of an emphasis on individual charisma, and charismatic leaders only need appear at the top of the ticket. A party with sufficient representation is free to fill out the bottom of its ticket with "specialists" whose expertise is valuable, but who wouldn't win a general election on their own.
Meanwhile in the states, every ticket is one member deep so there are no specialists, only generalists. While they can be advisors, the only official positions they can take are cabinet members (where we do see lots of scientific degrees). Further, the lack of scientists in low-ranking elected positions (like House of Representatives) means that there's less of a science+politics talent pool to draw from for the high-ranked positions (Executive branch).