Nothing to do with cooperation between B1G and SEC but more like common goals or shared ideals for how to win. Those two conferences don’t have to like each other, but, for example, they both will be able to vote for much higher player stipends which will give them an advantage over the lower P5 conferences that can’t afford the extra millions to make it happen.
Same thing happens in everyday life all the time. Pick two wealthy families in Sugarland and Woodlands then compare to two moderate middle income families in Pasadena and channel view. The high income families will have similar values on rules and laws for their taxes and money control most likely compared to the middle income families who may look for different types of financial laws or taxes.