Heh, some people always pull out the "there is no point, the market is saturated" argument when it comes to this discussion.
Yes, the market is filled with 4K monitors, but 4K monitors are NOT retina unless you go down to 24 inch size. I am aware of exactly one 4K monitor that can be considered retina, which is the Dell 2415Q. Even then, at 4K, your effective workspace is 1080p, which will be a significant downgrade if you're coming from 1440p (like everyone who previously used an Apple Thunderbolt display).
So, assuming you want a workspace of at least 1440p, you are looking at a resolution of 5K or higher. So you start asking yourself:
- How many 5120x2880 resolution monitors are on the market?
- How many of them are reasonably priced, say in the $2000 range?
- How many of them work via Thunderbolt and integrate well with recent Macbooks? The least you can expect is feature parity with your decade old Thunderbolt display, right?
After the first criteria, you have your options narrowed down to a handful of different models.
The Dell 8K is really targeted for enthusiasts, which makes the price too steep at $4000. Same goes for the Pro Display XDR. The Iiyama and Planar ones are decent, but they come from little known manufacturers and are not widely available.
So you end up with just one option, the LG Ultrafine 5K, before even getting to the third criteria.
And we haven't even gotten to the design aspect of things. Many people think the LG is ugly, but that is subjective. The fact is that the LG is made of lesser quality materials, and is quite wobbly as seen in many Youtube videos.
In reality, there is only one monitor that can replace the Thunderbolt display, but you must be willing to accept a few compromises. If you are unwilling to compromise, tough luck, better hope your Thunderbolt display doesn't die before something good comes up.
People loved the Thunderbolt display, I see tons of offices still using them.
I don't think it's due to lack of demand that Apple has not made a standalone 5K display. I think the reasons are technical. Remember Apple had to kind of "overclock" the signal timings just to get 5K signal to the iMac screen? That probably made a standalone 5K monitor completely unviable for Macbooks from previous years.
Now that Apple is back in the display business, I think the time is gripe for a new standalone non-HDR display. That said, I think 6K makes more sense than 5K, because iMacs have had 5K since 2014, and the Ultrafine 5K has been on the market now for.. 3 years? A standalone 5K display would seem a little outdated now, at least what comes to specs.