Seems like CF express cards are just as stupidly over priced as XQD cards though, I honestly can't see how a XQD card/CF express card, is any more expensive to make than an SD card, or certainly not to justify the price hike, I've never understood why camera manufacturers make cameras with unmatching slots, the same as when I had my D810, SD slot, and CF slot, bloody redicoulos ! now I have no need for CF cards, so have to sell them, fortunately I have a few SD cards [emoji849]
XQD, and now CFExpress, are more technologically advanced formats compared to SD cards, in any iteration, because SD is a format that has evolved over time, SD > SDHC > SDXC and now SDUC. Changes have been made to capacities and speed over those different iterations, sometimes physically changing the pin configuration to add more data throughput, but the underlying technology is not as advanced. All the time they have kept format backwards compatible, and using the same physical shape. All plus points.
The benefit of keeping the same physical size, and starting at a 'lower level' technology enabled the quick take up by manufacturers in many different devices, and for them to update SD card compatibility with new formats over years of device updates, as the advances have been incremental. The more devices that can use a format affects the price of the format, this is what has affected the XQD format especially. The cost of using newer technology also increases the cost as a new format, and not being able to take advantage of the 'economy of scale', also affects the cost to the consumer.
Hopefully CFExpress being used in a lot more devices will start to affect the prices to consumers in a positive way as time goes on. But an SD format will always have cost to manufacture advantages with whatever iteration they come up with because they can take advantage of the economy of scale for all parts used in manufacture because they are, and have been, producing cards to a huge user base, and many parts of the components of a SD card will not have changed much over the years. Sony Tough cards aside, I can't say I have seen a change in the plastics used in SD cards for many years for example, so if you can buy that in large quantities you can negotiate to buy it cheaper. Do that kind of thing for every component, and you have the option to pass that onto the consumer. Have multiple manufacturers competing in the market offering cards should also affect prices in positive ways for consumers. Many manufacturers producing cards in competition didn't really happen with XQD, and is only slightly better with CFExpress.
XQD had few manufacturers making cards for a few devices, using more advanced technology, that inevitably equals higher card prices initially. Prices staying high is explained above. Now that a format has replaced it, prices will probably go up as scarcity licks in.
It is up to the individual to choose a device that uses a new format or not, if the device offers benefits worth it to them, or the device added to the new format, offers something attractive to them as package. CFExpress builds on the XQD format, but needs devices to made for that newer format to be able to use the benefits, and unlike SD card changes being backwards compatible to at least use a newer card on an older device, XQD devices need firmware updates(if possible) to enable the use of CFExpress cards.
But why put two different card formats in one device? I can think of a couple few reasons.
The cost of adding two card slots using a new format may add significantly to cost.
The device may not have the processing power to use two card slots, with all the higher performance simultaneously.
You want to attract users to a device with a new format who may have many cards in a different format that would instantly become useless in the new device, potentially putting people off, having the option to use a different format will at least let users to continue to benefit from the cards they have, even if they may not be able to take advantage of all the devices features when using the newer card format.
There is not the need to initially have to buy more expensive cards in a new format with the new device if you already have carsd that may work with it, unless you want/need to use features which are only available using the newer format.
Until a new format is easily available, pairing it with a format as ubiquitous as SD, enables acquisition of a card almost everywhere in the world if needed. CFExpress, or anything else, will probably never be as successful and widespread as the SD format.
There are probably other reasons too.
As it is, it is up to the individual to buy a device with a new format, or multiple formats, or not.