[gweinberg]

Why did anyone want pear trees whose fruit is inedible and whose flowers smell bad in the first place?

[Turing_Machine]

They're dirt-cheap and grow extremely fast.

Just the ticket for fly-by-night real estate developers.

By the time they get big enough to cause problems, the developer is long gone, off to fleece other suckers.

[pvaldes]

Because they have a lot of convenient features. Specially that they are supernarrow in their first decades. Other traits weren't so much desirable.

Inedible fruit is a desirable trait in urbanism. Not necessarily a bad thing.