Why one railway gauge matters more than a wider freight gauge

Would a wider railway gauge improve the distribution of forty-foot containers on main lines?

One integrated gauge is preferred because it avoids transferring loads between incompatible vehicles; adapting the existing network is judged easier than widening it.

The preference is for a single integrated railway gauge, even when considering forty-foot containers on main lines. A compatible wagon can move between trains more easily than its load can be transferred between vehicles on different gauges. A somewhat wider common gauge would be acceptable in principle. Converting an established network would nevertheless be a massive project, making improvements to the existing infrastructure the preferred approach.