We don't have time to wait for a bunch of diesel engines to die of old age - as you know, they're quite long lived. And how long do you think is reasonable for diesel to be "phased out"? DEF became mandatory in the mid-2000s. It's been long enough.

At some point you have to draw a line and say, we're not going to allow something that spits out this much pollution just to make catching fish as cheap as it used to be.