I want to know what their motivation was behind these.

A forced single pull can be interesting if it has mechanics like Criterion trash packs or upper level Eureka Orthos mobs, but they don't in the DT dungeons. All it accomplishes is making us press the same bland buttons for twice as long. Was that the intended effect?

Was it to give players more opportunities to use their single target when there are 2 mobs?

I really don't understand.