Pure speculation - the person wanted to do maximum property damage - but not human casualty damage
They destroyed a major communications node between the coasts. The RV was parked directly over the main cable trunk leading into and out of the AT&T building.
They have built a bunch of new new sky scrapers in the last decade and are in the process of building a whole bunch more the last couple years.
I've heard one suggestion today that probably some one with a lot of money or some very crooked like a swamp dwelling politician would have no problem secretly blowing up a few old building to declare them unsafe so they could bull doze them down and build a whole new bunch of sky scrapers down town.