The problem is that the concept of “expert members” really translates to being an expert politician. The vast majority of the members of congress come from legal backgrounds, with a smattering of business based experience. Where are the scientists, the engineers, the educators, or industry experts? Basically, you have an institution that is filled with people who are experts at campaigning for reelection and working within the system as it currently exists to make sure that things within the system change as little as possible.
The problem is that the most powerful committees are full of people who have “seniority” and not the people who have the most relevant experience. If you don’t have a limit on how long someone can serve in a particular position, then age or experience become the default when it comes time to choose people for specialized positions. The respective presidential nominees are a great example of this concept in action. In most cases, things devolve into a simple “it’s my turn now” decision making process within each party.
Look at the current Committee on Space, Science, and Technology for example. Lamar Smith is someone who admitted that he abandoned a career in science after taking a freshman science class and instead choose to pursue a career in law before becoming a life-long politician. Nothing against Smith personally, but wouldn’t the country be better served by literally any scientist in the country serving in that position, as opposed to someone who has done nothing but politics and law for the last few decades?