When a market with competition becomes a monoculture, every security problem that used to affect only one product becomes a class break[1] that affects everything. Just like the potato famine, software monocultures can fall to a single attacker, who also benefits from the consistent interface.

> What is special about browsers

Nothing. We need multiple implementations of all software that is relied upon for anything remotely important. It still amazes me that so many businesses critically depend on something that is only available from one source. Without a second source[2], the business lives or dies at the whim of the company they depend on.

[1] https://www.schneier.com/blog/archives/2017/01/class_breaks....

[2] https://en.wikipedia.org/wiki/Second_source