This is dumb, because there are a ton of drive cages that fit in a couple of 5.25" drive bays, contain a backplane, and either SATA connectors or an SAS connector. Easy example: https://www.newegg.com/athena-power-bp-tla3141sas12-other/p/N82E16816119046?item=9SIAZ8XJ1U6752
So the idea that there's no demand for this just can not be true, since people are literally making the hardware, just not the piece of metal to wrap around the drive cage so you can set it on a desk.
Does anyone make a high quality eSATA enclosure? I honestly don't even care if it's hot swap. I do not want a SATA to USB enclosure because I do not want an ASmedia or JMicron controller. I just want a backplane and an eSATA (or Mini SAS) connector. I am aware that Synology makes something like this, but I think their connector is proprietary. OWC makes some thunderbolt enclosures with in Intel chipset, but the design spec also includes a JMicron controller so I question the reliability.