The answer, I think, is almost certainly to reduce stresses associated with the sharp ends of the chevrons in the grousers, although the wheel designs differ in other details as well (see below).
As is well known, Curiosity has suffered a significant amount of damage to its wheels. Quoting from the reference above:
The tears result from fatigue. [...] The stresses from metal fatigue are highest near the tips of the chevron features, and indeed a lot of tears seem to initiate close to the chevron features.
(Note that there are punctures in the skin as well, which are I believe not fatigue-related).
It's well-understood that stresses are high around sharp corners in structures, and thus avoiding them can reduce stresses, and that this can result in fatigue failures. Famously the de Havilland Comet suffered from fatigue failures which caused a number of accidents: an extensive document on this is here (PDF link). These fatigue failures were caused by high stresses around the corners of the windows in the aircraft, which were square. The aircraft was then redesigned with round windows, which solved the fatigue problem. None of this was helped by fatigue not being well-understood at all at the time. (Amazingly, Nevil Shute's novel No Highway describes fatigue failures in aircraft, and predated the Comet disasters. Shute was an aircraft designer.)
So I believe that avoiding the chevron pattern avoids the sharp corners with associated high stresses which have caused trouble with Curiosity's wheels, although they have not been the only source of trouble. However I have not been able to find direct confirmation of this, and there are other design changes as well: this page describes some of the changes, which include the tire being thicker, presumably to reduce puncture damage.
A couple of entirely unsourced notes: one feature that is noticable (and is documented) is that there are more grousers on the new wheels than on the old ones: the spacing is smaller. This will do at least two things: it will mean that the load on the wheel will be spread over more grousers, thus reducing the stress around each grouser, and it will also mean that any stone which can get between the grousers in order to puncture the wheel structure needs to be smaller, as the spacing is smaller. Both of those factors are clearly a good thing, although they must have cost mass.