Spare parts of lack there of. Faster blade erosion, doors to narrow to support infantry as they unload. High operating cost.
Got me more curious so I went to look and found this on the wiki.
"In 2010, German tabloid
reported that German Army experts had concerns that the helicopter was not yet ready for the transportation of combat troops. They stated that the seats were rated for only 110 kg (240 lb), not considered enough for a fully equipped soldier. Heavy infantry weapons could not be adequately secured and the cabin floor was prone to damage, citing an anecdote of damage caused by footwear. The helicopter could land on only firm ground, with obstacles not exceeding 16 cm (6.3 in). Troops carrying full equipment could not use the rear ramp due to weight-limitations placed on it. Adding a door machine gun was not possible due to space taken by troop ingress and egress; there was also no provision for fast roping or paratroop equipment.
In response, the
proclaimed that this article referred to a prototype, not to the production model; the specifications for which were not even finalised at the time. The prototype evaluation and its results were described as a normal procedure in an ongoing design process.
In November 2011, the MRH90 program was placed on the Australian Department of Defence's "Projects of Concern" list.
The most serious problem identified by a diagnostic review, which caused a brief grounding in 2010,
is
rubbing caused by the bending of a spool in the
engine due to uneven cooling after shutdown. Other problems identified include failure of transmission oil cooler fans, windscreen cracking, an inertial navigation system that is slow to align, and the weakness of the cabin floor to withstand the impact of soldiers’ boots – a problem also encountered in German service.
In March 2014, it was announced that a Dutch NH90 had suffered higher than expected fuselage wear and corrosion following an extended deployment at sea; analysis by the Dutch National Aerospace Laboratory attributed the corrosion to design and assembly flaws. However, the aircraft were not grounded. In response, NHI Industries launched a corrosion prevention programme and enacted several design modifications.
In December 2014, Dutch NH90 deliveries, which had been temporarily halted earlier in the year, restarted after the majority of identified points were addressed and an agreement was made by the manufacturer to bear the cost of developing modifications, repairs, and preventive measures against corrosion.
The operating cost of a NH90 HCV (High Cabin Version) was reported as being at least 242,000 SEK per hour flown, or about US$28,000, in 2018"
Yeah, seems like the Z-20 was a good choice.