Could be right, I thought it had something to do with the sun, imagine the throwers throwing into the sun.
I looked up the IAAF Track and Facilities manual, it is all about uniformity, also found this regarding the 200m. Hope they don’t mind it is a copy and paste.
On occasion in the World Cup in Athletics there are 9 teams requiring 9 oval
lanes. This is the maximum number of oval lanes that should be provided at a facility
as otherwise there is too much advantage gained by the athlete in the outside lane in
a 200m race over the athlete in the inside lane. Further the outside lane could infringe
the World Record rule that states the record should be made on a track, the radius of
the outside lane of which shall not exceed 50m.
It is permissible to have any number of sprint lanes on the straights.