There is a vast difference between 6 mini hubs and 2 major ones, especially when different airlines have different mini hubs. It’s a lowest hanging fruit change especially and airlines are trying to minimize hops which really makes a difference.
Remember, mini hubs are near major destinations so people are very likely to be starting or stopping at one, Combined with different airlines 1 hops vs 2 or 3 is common, but more so 2 hops vs 3 or 4.
What has actually happened is that hubs became more numerous and smaller. A major airline might have 6 hubs instead of 2. And most long distance trips are done with 2 legs instead of 3.