According to the following document, Taiyo Yuden discontinued EYSHSNZWZ and other modules because business related to WLAN and Bluetooth modules haa been transferred to another company.

https://media.digikey.com/pdf/PCNs/Taiyo%20Yuden/UTY-DN21-07D_05-Nov-2021.pdf

Yes, it's quite simple: to optimize profits.  You could always build your own if you must have that form factor.  However, I think they are selling the product you want but the lead time is just under a year.

EYSHSNZWZ

Hm, I was more looking for the reason it had been marked it as discontinued, but thanks for the guess. Great idea, I'll have to try building my own when I get my personal foundry up and running!

It's not a guess, this is how publicly owned corporations work, they always optimize for profit.  It's unhelpful but also correct.

The only way to find out the underlying reason is to contact the company that discontinued it, it's not like industry insiders hang on out hackaday.io.

Computer based assembly is entirely possible (it's a WLCSP nRF52832 with extras) but not with your average PNP machine as it's really just a package-on-a-package which means there's no need for a foundry.  If you MUST have one of these then you can buy one for extortion-level prices (~$500) here: https://www.utmel.com/productdetail/taiyoyuden-eyshsnzwz-9712215

Just FYI,  the package on package route is viable as they provide the schematic in their documentation: https://www.mouser.com/datasheet/2/1113/TY_BLE_EYSHSNZWZ_DataReport_V1_5_20190606E-2905887.pdf

and there are services to PoP assembly services: https://www.pcbcart.com/assembly-capability/package-on-package-assembly.html

The questions to ask now are how badly you need this part and how many do you really need.