Because the SI unit is meters per second, so maintaining the “second” gives people with that understanding a basis in which to compare the delta-V.

I'm genuinely curious whether there are a substantial number of people out there who deal on a regular basis with dV's on such a minute scale. Who would that be, outside an asteriod-redirect program such as this? Satellite operators doing precision trajectory correction?

I found the meter per day conversion helpful. Through another lens, it's about 0.000036 km/hour (or about 1.5 inches per hour).

Okay but they didn't give it in meters per second, they gave it in micrometers per second. Converting to micrometers per second is exactly as much arithmetic as converting to meters per day.

No, it is not. It is in fact no arithmetic at all, if you understand how SI works.

Is it 1mm/sec?

no, what? µ is the dimensionless number 10^-6, just like k is the dimensionless number 10^3.

And you are doing what with that dimensionless number? Multiplying?

Yes, it's one multiplication in both cases.

Multiplying/dividing by 1 million is way easier than by 86400 though.

I would argue that multiplying 10 by 86400 is just as easy as multiplying 10 by any other number. Hint, it's the same as multiplying a number by 10.

One would think that any nerds that knowledgeable could divide by 86400 to make the article more accessible for the rest of us though.

1.22337962962963e-21 light years per second!

1 meter per day is something most people can understand. But even more relevant would be 1 Earth diameter in 16,000 years... which makes it very clear this isn't useful for saving the Earth from asteroids yet.