The A320neo and the Boeing 737 Max use larger turbofans for increasingly higher efficiency gains. These larger engines would be scraping on the ground with the original 737 design, which is why the engines had to be mounted further forward and higher on the wings. This is what changes the flight characteristics, leading Boeing to develop the MCAS system to make the plane fly like the older 737s, which famously led to two crashed planes when it malfunctioned.

The Airbus A320neo did not run into this problem because the landing gear for the A320 are longer and it sits much higher off the ground, so throwing on the larger turbofans still left them with plenty of ground clearance.