That explains why they’re making the new one!
In the wake of the announcement of a fourth Marvel vs Capcom game, Marvel vs Capcom Infinite, as well as the port of Ultimate Marvel vs Capcom 3 for current generation systems, Capcom have gone ahead and shared sales numbers for the entire series, which demonstrate just why Capcom are keeping the series alive, in spite of the licensing issues involved.
Capcom have confirmed that Marvel vs Capcom games have sold 7 million copies worldwide, which is an excellent number for a traditional fighting game series. Fighting games usually sell fairly low, unless they are Smash Bros. or Mortal Kombat, and Capcom are undoubtedly happy with the result- which would also explain them making a new one.
Marvel vs Capcom: Infinite is slated for next year for Xbox One, PS4, and PC; meanwhile, Ultimate Marvel vs Capcom 3 is available for PS4 right now, and it will be coming to Xbox One and PC early next year.