As
@Cashmonee suggested, someone likely to purchase the Mac Studio also is likely to look for a monitor (or even monitors) specialised for what they're doing.
When I look at the specs of the iMac displays I see Apple trying to strike a decent balance for a lot of various applications, at the cost of having some drawbacks for any one of them, which makes total sense in my opinion for an integrated display. For an external display (the Studio Display), perhaps for users whose activity covers a diverse range of applications, or less "power" users, but not for more specific ones.
Whether that's for photography (retouching, development, printing), video (editing, grading, etc.), productivity, coding, for each one of them the Studio Display's spec sheet makes you go "this is great, but that is meh".
To be honest I find it weird that this display was mostly shown alongside the Mac Studio. I bet that a lot of Mac Mini or MacBook users will be interested and maybe even comprise most of the people who will buy it.
So, a more concrete illustration. I do quite a bit of photography and like to proof the results on my monitor before printing, and when you do it right that's even possible for me to get a good preview of what an external printing lab will produce. For that application I use an Eizo monitor regularly calibrated, and I absolutely wouldn't want the Studio Display for it (not enough Adobe RGB coverage + not as easily calibrated in the long run as the Eizo monitors).
But that monitor's contrast ratio isn't particularly great (although no worse than the Studio Display), its coatings makes for a rather poor viewing experience for video - particularly in darker environments, and is quite unrepresentative of most displays people watch content on these days. Lately I've been looking into something better suited to video content consumption / creation for darker environments. Neither is the Studio Display superbly suited to that task as far as I'm concerned as its contrast ratio isn't good enough (nor the XDR for that matter given the lack of zones). It's likely to be be an OLED / QD OLED monitor as I'm not expecting local dimming backlights to reach the desired density for larger screens in the short term (and I'll wait until late 2022 as this is a cornerstone year for displays).
I'll end up at home with three different displays (MBP, Eizo, OLED/QD OLED monitor), each best suited for different applications. To be frank I'd have added the Studio Display to it either if it were priced at a more impulse buy price (if only for ease of use and ecosystem integration, for regular desk usage), or if it had been slightly more expensive and featured a 500+ zones local dimming backlight.