My guess is the two lanes merging into one are only getting one lane. That is, only one lane is added after the merge, and both overpass lanes are merging into the one new lane.

But if there are indeed being two lanes added due to the merge, agree that doesn’t make much sense.

If the former, also agree that they should’ve added two lanes instead of one. But that decision could’ve come down to physical limitations, cost, or something else.