The removing and reinserting the SD is one of the main points of failure.The socket and carrier are both very thin lightweight plastic so the second more often failure is the 2 piece SD shell falling apart.
The post above about not having the card in slot 1 was saved by slot 2. But the camera will not shoot without card so that would not have been a lot of images, it reminds you right on the screen that you forgot a card. In the Z7 one never has to remove a card, its high-speed USB -c interface allows fast transfers to a storage device, faster than current card transfers
Regarding the D7500 not having a secure card...it is a different class of camera, it is not targeting advanced hobbyist or pros. Commercial photography is not the customer base for that camera when the best pro crop camera available is only a few hundred dollars more; D500. ALL Nikon pro camera have XQD for a few reasons so it is an additional indication of how Nikon targets the Z series.
The D5 and Z7/6 are both made in Japan at the Sendai plant which is oriented towards their highest end cameras. The Z7 IS a pro camera and built like one, unlike the Sony a7 series which is definitely a hobbyist camera build like an entry level. The D500, 850, 5 and Z are not for everyone and the D7500 was focused on hobbyists who wanted the speed and IQ but light cheaper less mission-critical body. For general photography, the D7200 is still hard to beat as a balance of price, flexibility, build quality and IQ that no other camera I know of has. It is the Toyota of cameras, whereas the D5 is the Ferrari, for most users the Toyota is just a better car. Nikon has indicated they will have a Z pro action sports camera so it makes sense they will have lower end Z mounts lower priced cameras also.the Z6 is really competitive for the advanced and general purpose pro-semi pro field, a rugged fast camera with most of the features of Z7 that costs $1000 more. The lower end body might have 2 SD slots, and the action, wildlife, sports version will have 2 slots possibly because action shooters do a lot more high count bursts and they are more likely not having high-speed backup available. It is all about choice and people understanding what they actually need.