Speculatively speaking:
Global News suggests that the problem is Horseshoe Bay terminal, as larger ferries can't be supported on that end.
Which is true. I'm not sure why people would commute from Nanaimo into Vancouver, but they do. They certainly wouldn't if they had to go all the way through Tsawwassen.
This probably puts the "build a bridge" (for truck traffic) back on the radar.
http://www.th.gov.bc.ca/Publications...fixed_link.htm
Notice there's a "Nanaimo to Richmond(YVR)" suggestion that could still be a ferry route.
A fixed link however is somewhere in the 8-12 billion cost. 200 million to upgrade the ferry terminals is a drop in the bucket by comparison.