Brands have compounding value.
The more success the brand has had the more valuable it is, because the streak is longer and the more the owner has to lose by breaking it.
If the brand starts giving leverage, it makes sense for the owner to invest in it more, and to the extent it's still useful, it becomes even more useful.
Because branches have power-law returns, reputation is partially noise-driven and then self-fulfilling.
The brand has to stand for something.
Successful brands are tempted to dilute it to cash in on brand value and trust.
Brand is trust, distilled.
An eponym stretches too far over time to still mean the specific brand.
A metonym over time dilutes to not have any of the original promise of the brand.