Maturity of model. They're trying to compete with the Ernst & Youngs of the consulting world, but don't end up selling projects -- they sell resources (at least in the US) . This results in multiple submissions/interviews with clients instead of simply bidding for the work and assigning whichever people are most applicable -- wastes time for client and consultants. They'll basically remain a staffing firm until this is addressed.
While on the bench other consulting firms have people work on internally billable projects -- that is, they're not dead weight and are actually providing "paid" service. Sia does not have any internally billed projects so you're basically on borrowed time. This translates into pressure to help find your own role after a while.
In mature consulting companies the higher level you go the more diversified you become. A Sr Consultant might be on 3 or 5 projects, each getting a few hours a week of their time. A Manager might oversee 10 -15 projects, each getting an hour or two of their time. Sia doesn't do this. Everyone needs to be 100% billable to a single project -- while senior people also are required to do their account management, business development, mentoring, etc. It's very odd and puts everyone in a silo, rather than in logical business units.
There's a lot expected outside of your full time consulting role (even if you're not a manager). There are Working Groups (with assignments, initiatives, meetings, presentations), the Career Advocate program (a sort of mentorship initiative), DEIB groups (also with commitments), a variety of all-hands meetings (from Paris, US headquarters and local office leaders), happy hours (not required).