Why can't it be something simple?
Because monitors aren't simple. There are dozens of axes along which they can be scaled.
They have resolution (1080p FHD, 1440p QHD, 4K, 5K, 6K, 8K), aspect ratio (16:9, 8:5, 4:3, 3:2, 21:9, 32:9), refresh rate (60 Hz, 75 Hz, 120 Hz, 144 Hz, 165 Hz, 240 Hz, 360 Hz, 480 Hz, 1 kHz, and of course adaptive refresh rate tech including G-Sync), colour quality (depth and accuracy), contrast ratios for HDR, panel technology (LCD-TN, LCD-IPS, LCD-VA, OLED, QD-OLED, WOLED, and now RGB stripe OLED), backlight technology (CCFL, edge-lit LED, miniLED, microLED), connectivity (HDMI/DP, USB-B, USB-C, DP alt mode, Thunderbolt, 3.5 mm, and KVMs).
It's very hard to stuff all this information in one neat model number.
On the consumer's part it makes sense to understand these features and what is necessary for one's use case, filter monitors by said features, and note down the model numbers that satisfy the requirements.
There are only ~5 flat-panel manufacturers worldwide: AU Optronics, Innolux, LG Display, Samsung Display, Sharp Display, and recently BOE Display. Apple has to use one of these, even for its bespoke, notched, curved iPhone/iPad displays.
This new 5K 2304-zone panel was developed by LG Display, and is not 'generic white-labelled slop' by any means. It is an extremely good panel in its own right, probably the bleeding edge of LCD technology today achieving top-notch responsiveness, contrast, and colour depth and accuracy.
That MSI monitor will probably retail for ~£800 as will the Asus and LG equivalents, which is not a trivial amount for a monitor. Apple just marked it up 3×, as they are prone to do for anything.
Back in the day (~15 years ago), when 4K monitors were unheard of and even Apple's high-end displays were still 1440p, you could get a bottom-dollar monitor using one of their panels (e.g. Yamakasi Catleap Q270) for about a third of the price. However, it came with no amenities, a single connector (dual-link DVI only), a questionably legal power cable, and no built-in scaling. The vendors, presumably to prevent refunds, even asked for your graphics card model before selling it to you, because it wouldn't work with low-end cards. Oh, and there were very few in the U.S., so you were typically getting them shipped straight from abroad, customs duties and all.
We've definitely come a long way.
After a few years, the "cheap ones" have usually caught up, if you're willing to do the research.