While I suspect ISIS doesn’t set up a motor pool the way the US Army does, at any event, they tend to be an area target. Normally, an area target would call for an area weapon, such as the Mk20 Rockeye cluster bomb.
But due to the dud rate of cluster bombs, and the resulting threat of unexploded ordnance to innocent civilians, the US is reluctant to use cluster bombs. Other countries have signed a ban on them, but the US has not. But they have been notably reluctant to use them.
So how do you cover an area target if you can’t use cluster bombs? You could simply use a bigger bomb. But that’s not terribly effective. The largest bomb in routine use is the Mk84 2000lb bomb, and the various guided versions, JDAM, LGB and whatnot, that use the Mk84 as a warhead. The effective radius of a Mk84 against a soft target is pretty hefty, but not terribly much greater than a 500lb Mk82. As a general rule, you’ll cover more area with 4 Mk82 bombs than one Mk84.
The bombs seen in this clip were almost certainly either 500lb JDAM bombs using a Mk82 warhead, or, possibly, 250 pound Small Diameter Bombs, or SDBs. The nice thing about the SDB is that its very compact design means a single strike fighter can carry quite a few of them.