The change will reduce the amount of tire sets needed during a weekend by 2 per car. It's a (small) move towards sustainability that has very little impact in the sport itself...

"This means a reduction - from 13 to 11 - of the sets of dry tyres that each driver has available for the entire event, therefore decreasing the environmental impact generated by the production and transport of the tyres"

In general I agree but the transparency level shown by the Cities Skylines 2 team has me rethinking this.