That “source” does not support the claim that customs is the bottleneck, it supports the claim that port operations in their totality are the bottleneck.
The answer to this question is that merely possessing coastal land is not a sufficient enough condition to open a port-- rather various levels of government are involved in creating and regulating an official "port of entry" to the United States.
Otherwise, you would have people bringing in nuclear bombs in the cover of darkness at a port that doesn't have government agents operating at it, no?
If we had more ports, we would have less bottlenecks. But we can't have more ports, because of inefficient operations.
Big Sur and the Mendocino coastline make for poor port sites.
Every major harbour site (and several minor ones) that can be utilised is: Seattle/Vancouver (Puget Sound), Portland (Columbia River), San Francisco, Los Angeles/Long Beach, and San Diego.
Even the minor sites of Coos Bay (Oregon), Monterey, and Morro Bay have some cargo capacity (lumber at Coos, largely fishing out of Monterey and Morro). None of those are remotely near large population centres or other transportation infrastructure, and would make zarrow sense for a major port.
Seattle, San Francisco, Los Angeles, and San Diego are major destinations on their own, and are well-connected to major land-based transportation links (rail and highway).
If the original output was acceptable, he wouldn't have had to do that.