Portfolio managers, if they're even the least bit renown in the industry, are often promoted at distributors or in fund marketing material. In my observations, this is mostly pertaining to equity mutual funds: especially fundamental strategies (not quant) where stock-pickers can strut their stuff if you will. While most can't outperform the market, the few that can, can really prove their worth the management fees, delivering double-digit returns over a decent holding period.
Meanwhile, MMFs by comparison seem sleepy and boring. We're not talking about much beyond the risk-free rate here. That said, operating a MMF doesn't seem so easy. Lots of the short-term instruments in the MMF portfolio seem to require almost an active approach to management. Maybe "active" is a stretch, but at least comparable to an authorized participant of an ETF or thereabouts. Point being: though a lot is in guaranteed/quasi-guaranteed debt such as treasuries, agencies and CDs, there are sprinklings of credit exposure. We've seen large MMFs break the buck before in the GFC.
So all this leads me to believe that the MMF PM is an important role, despite the fact we as investors hear very little of him.