Yeah, I was wondering the same thing the last two months when I was digging through all suitable options for a new build.
In some cases, it looks like it was an easy addition to "make them stand out" with the latest WiFi 6(E). Then everyone jumped on board and put it on EVERYTHING (not just the Preium, but the mid boards and even the low boards as well). And in all honesty, I have zero use for it as I hardline everything. But there are little to no options, especially on the higher end motherboards that do not come with WiFi these days it appears, pushing up the price for their addition.
And that's what I think the reason for their inclusion is; keeping prices high.
This was why I took a while to decide on grabbing the Asus Proart X670E, yeah it had WiFi6E, etc. And since that was "standard" I had to look at other inclusions to justify the price. Thankfully this Proart had 10gb ethernet included, as well as Thunderbolt/USB4. Which if purchased separately, made sense in terms of cost. Especially if I was going to get a stonking 4+ slot GPU down the line, making the extra PCIe slots redundant for expansion cards.
Personally, I don't mind their inclusion, but would definitely have liked some options (choices) without them as well.