The Goldstream section of the Malahat is one lane in each direction.
The mountain next to it climbs to over ~350 m above sea level.
The area consists of metamorphosed sedimentary and volcanic rocks with a varied mix of greywackes, tuffs, and fine-grained volcanic and sedimentary units. In other words, any construction or tunneling work would be particularly difficult and extremely expensive. The latest estimates to add lanes in this section would be $ billion's, and even more to tunnel!
On top of that, any construction project here would impede traffic for several years since the work would need to be conducted from the roadside as indicated in the current projects documentation.
The Damage to the Park from such construction would be unforgivable.