I often research camera gear, just to see what is ... (
Yes, some people feel the need for two slots, like the D7200 had and, for some reason, Nikon deleted from the D7500 that replaced it.
The thing is, it's not just the D7500's single memory card slot...
D7200 was 24MP while the D7500 is 21MP. This was probably done so that the D7500 could accommodate 4K video, where the D7200 was limited to HD.
DXO also rates the D7200 to have slightly
higher color depth and about 1/2 stop more dynamic range. On the other hand, probably thanks to the reduced resolution, the D7500 has slightly higher ISO usability rating and one stop higher selectable setting (though it's probably higher than you'd ever want to use).
The D7500 uses the same battery as the D7200, but is rated to get around 15% fewer shots with it. Something closely related to this that might be of concern to some shooters, for some reason Nikon also deleted the D7500's compatibility with a battery grip and doesn't offer one for use with it. The previous D7100 and D7200 models can optionally be fitted with MB-D15 grip to double battery capacity at the same time it provides a vertical grip and secondary controls, whichare quite useful when shooting in portrait orientation. Yes, there's a very inexpensive third party grip from Vello for the D7500... but it DOES NOT allow a 2nd battery to be used and it lacks most of the controls. It only provides a shutter release button and that has to be connected using a funky external wire to the remote release socket. Likely Nikon deleted the D7500's compatibility with the MB-D15 as a cost saving measure and so that it wouldn't compete too closely with their own more expensive D500 model (which does have capacity for a Nikon-made grip with full controls and 2nd battery). While these things may not matter to a lot of users, I can't help but wonder if it's cost Nikon some potential customers for the D7500.
Some of the exterior panels that were magnesium on the D7200 are reinforced plastic on the D7500. This reduces the newer camera's weight a little and doesn't seem to effect the feel of the camera or change weather resistance.
In spite of the above, there are some definite upgrades in the D7500 too...
It offers 8 frames per second continuous shooting versus the D7200's 6 fps.(But, for some shooters this increases the need for a battery grip and increased battery capacity.)
D7500 has Nikon's Anti-Flicker, which is very useful shooting under fluorescent and similar types of lighting. D7200 didn't have that feature.
While both D7200 and D7500 use a very similar, excellent 51-point AF system, the D7500's got a few new tricks such as additional, user selectable AF point groupings. D7500 also got a chip upgrade and has a more advanced AF fine tuning feature. The touchscreen of the D7500 also can be used for AF point selection and even to trip the shutter, when using in Live View.
The D7500 got an articulated (tilt) rear LCD touchscreen, which the D7200 lacked. However, on D7500 that screen is a bit lower resolution than the fixed screen in the D7200. It's not enough difference in resolution to be noticeable most of the time, though.