Seemingly excess trace length reason
This is an example of length matching (which can be necessary for both differential pairs and certain interface bus types).

This is done so that a set of signals that are launched together arrive within a short time of each other (how much they can be off depends on the timing error budget available); note that no amount of length matching will guarantee perfect timing across the matched group due to various effects (even manufacturing tolerances have an effect here).

Although the signals in question are highly likely to be impedance controlled that is a separate subject; the length match is specifically for timing; impedance controls are to maintain signal integrity.

It is certainly true that no amount of length matching will be of use if there is a failure to properly implement SI where it may be required.