Who pays $70 for new MMWs anyway? It's all bought at a discount, either in advance or after release.
I assume anyone interested in Captain Marvel MMW (at least from Vol 3) also has Adam Warlock Vol 2 (This is my case, I don't have Captain Marvel Vol 1-2 nor Adam Warlock Vol 1), which argues against inclusion.
However, it's obvious that these two stories will raise the profile of this volume due to the Avengers film popularity and I guess it's more marketing savvy to cater to new buyers than just the existing pool. And Warlock Vol 2 can't be found for cheap either.
While as a customer I was against the inclusion, I'd probably have done the same as an editor.