Not all forms of sortition are based on volunteering, sometimes it’s proposed as a civic duty similar to jury in the States. Volunteering introduces a selection bias which could make the system unfair.
The main issue with it in my view is that in present-day society there’d be many attempts to influence the committee (read: corruption). Of course this also applies to representative democracy, but that doesn’t make it any less of an issue because that’s one of the major problems with representative democracy that needs to get fixed.
I can easily picture a dystopian implementation of sortition where the public sees it as a lottery where they can get rich by getting selected and taking bribes from corporations once they’re in, much the same way American representative democracy currently works (and to a lesser degree, representative democracy everywhere).
This would be a big problem for capitalism, but thankfully it’s 30 years in the future making it impossible for capitalism to foresee.