Re: It's about pork
The problem is that the market for BFR-scale payloads is smaller than for Falcon-scale payloads (modern electronics allow for smaller satellites). This means that it will take a longer time for the BFR rocket to accumulate the same number of successful unmanned launches as the Falcon has (approaching 50).
If it costs less to fly the same weight on BFR than Falcon 9, as Musk has claimed it will, why wouldn't customers switch to using it, even if they're massively under-using the vehicle's capability?
And if that cost can be cut further by using some of that extra capacity with ride sharing, that would surely sweeten the deal even further. In other words, I don't see why most clients won't switch to BFR almost immediately.
There may be a few that want to stick with the F9 because it is known to be reliable, but that attitude won't last long; if you want proof, look how quickly SpaceX have been able to get people switching to re-used boosters.