TL;DR: Who says that many relatively more experienced or outstanding academics are often not involved in these committees? There are, but with some limitations. Usually, membership is by invitaton.
I'll limit my answer to technical committees of international organizations, according to my limited knowledge, in particular those related to my field.
First a few remarks:
- Most technical committees work on the redaction of standards, regulations, best practices, recommendations, testing procedures, compendia of terminology, recipes to concoct witch's brews, etc. related to different technical and scientific activities. They can also suggest directions of research that can be particularly important in a certain epoch. People working in these committees should have a broad view of their field, but also a capacity for understanding the practical impact of their normative activity and, possibly, an eye toward the future. Not all academics have such kind of broad knowledge.
- It's not really true that experienced or outstanding academics are not involved in these committees: if you have institutional access to IEEE Xplore you can browse through the standards and have a look at the people who redacted them. You'll probably find many renowned academics. I'll give other examples below.
- The activity of many of these committees is time consuming, frequently boring, and, honestly, not very rewarding if you think at how this kind of documentation is regarded by the layperson (if you're lucky, you might be considered part of a faceless committee; others who have to comply to the regulations devised by a committee might use less gentle words).
In addition to the above remarks, it should be noted that some institutions have constraints on the participation to their technical committees that might not be met by academics. I'll expand on this by taking a few examples from my field, that of metrology (no worries: if you don't know what it is, I won't blame you).
Metrology is organised in international committees which work under the umbrella of the Bureau international des poids et mesures (BIPM).
The first scientific committee that we meet by walking down the hierarchical structure of metrology is the Comité International des Poids et Mesures (CIPM). The members of the CIPM are elected by the Conférence Générale des Poids et Mesures (CGPM). The requirements needed to be part of the CIPM are quite stringent: you can read the criteria in the pdf linked on this page. Among the required personal attributes and qualifications, as reported on pp. 2-3, I'd like to highlight the last two:
- Each member should be able to make a significant commitment of time and energy in support of the activities of the CIPM and the Metre
- Each member should have, in principle, the financial resources required to attend meetings of the CIPM.
- Candidates should commit themselves to serve until the end of their term.
Government Support and Relationship
- In accordance with the discussions at the 17th CGPM, each candidate should have at least tacit support from their government to serve on
the CIPM. Each Member should maintain a good relationship with their
government and the leadership of their national metrology system
throughout their membership on the CIPM.
Thus, not only do the members have to be excellent scientists, but they should also have good relationships with their government, and be able to devote a significant amount of time and of their research funds to their role. These requirements are probably beyond the possibility of the average faculty, and most of the CIPM members are, therefore, directors of National Metrology Institutes (NMIs). Those, among them, who are faculties typically have a double affiliation, being also university professors (list of members). Among the former members you can probably find other renowned academics, and a few unsuspected Nobel prizes.
Thus, again, it's not entirely true that experienced or outstanding academics are not involved in these committees.
The CIPM comprises many other technical committees called Consultative Committees of the CIPM (CCs). Also here we can find the criteria for membership of a CC.
Notice that here the membership is open to institutions, not really to individual members:
Membership of a Consultative Committee is open to institutions of
Member States of the BIPM that are recognized internationally as most
expert in the field.
Unless you are
named individuals when their knowledge and competence are highly valuable to the CC, even if they come from an institute that does not fulfil the membership criteria.
So, generally speaking, faculties, even excellent ones, cannot be member of the CCs because the institutions will nominate, as representatives, researchers from their staff. For a faculty to be invited as a member, their knowledge and competence should be highly valuable to the CC (and, I'd add, not available within any NMI).
Continuing to walking down the complex hierarchy of metrology, we find the technical committees of the Regional Metrology Organizations (RMOs)
For instance, EURAMET is the European RMO, which, among various activities, provides funding for joint projects among the NMIs. Its technical committees are listed here. Also these technical committees require their members to be part of NMIs, but groups working on a certain specific task can invite external people, like academics, to be part of the working group (not of the committee). The invitations usually come from the need of a specific expertise, or simply because someone propose an idea that could be of interest to them.