Why do we keep using it?! It’s so unscientific that it embarrasses me that intelligent people even talk about it.

Fabs have been increasing transistor performance without shrinking the size much; for example, a 22 nm FinFET has similar performance to a 14 nm planar FET so feature sizes don't tell you as much as they used to. This led fabs to invent "effective" feature sizes to convey improvements in the process.

It’s basically like a version number now I suppose.