in automotive world you always need 2 suppliers in most cases and in tire business imagine that bmw would rely only on 1 business especialy in the start of manufacturing when demand is the highest? they can not afford the production to stall if there is shortage of components or if will supplier closeses the business he needs a plan. they make arround 100 cars per day- 400 tires minumum needed per day
and where are spare parts. i believe both are great and wont disappoint.