With SR 92, probably the main issue was that I-15 through Lehi (Lehi Main to 92) was the last to get a full reconstruction and expansion this century. The CORE project reconstructed I-15 from Spanish Fork up through Lehi Main St in the early 2010s, and the Point project did the same from southern Salt Lake County down to just before the 92 interchange in the mid-2010s.
If I had to guess, that last section in northern Utah County probably had to wait until enough had been determined as to how the Mountain View Corridor project (i.e. 2100 North) was going to connect with I-15. When that DDI was built in 2011, the Mountain View project overall was in its infancy - there was no road in Salt Lake County yet, 2100 North had just barely opened, and likely a lot of ideas for what the ultimate plan would look like were still up in the air. No sense in spending a bunch of money on a full I-15 reconstruction if you're going to have to tear up half of it for whatever you ultimately decide to do with the 2100 North connections. This way, after some more detailed plans had more or less fallen into place by the late 2010s, UDOT could kill two birds with one stone and reconstruct 15 in a futureproof way that allows for easily upgrading 2100 North when that time rolls around.
Of course, by the early 2010s, that area around the SR 92 interchange was already growing by leaps and bounds, and the farms and cows that used to dominate that area were rapidly being replaced with new Silicon Slopes development and offices and subdivisions. Something was needed that didn't involve spending a bunch of money on a bridge that might have to be replaced again in 10 years. Hence the DDI - which, I'll give it credit, was better than the earlier diamond.