May I ask a stupid question:
Why does anybody bother reverse engineering the STLINK when you can buy the latest 24MHz one (V3) for about 30 quid?
For a variety of reasons:
To learn by using something a person already has (Blue Pill, Maple or a clone)
Because a V2 clone can be flashed into a J-Link, much more powerful than even the STLink V3
Because the price of a STLink V3 depends on where you live, and in some places price+shipping is 10x the cost of a clone
Because for most debugging purposes, especially on a low end processor (STMF1-F4), the speed of the debugging probe is irrelevant
Because until recently, the V3 was not available, and a V2 clone was by far the best way to get started
Because, apart from the VCP (which you can anyway simulate using a separate FTDI USB Serial), the V3 doesn't offer anything more than a V2
A V3Mini is even cheaper, but once again only recently became available. These days I would probably recommend a V3 over any V2 clone
For someone developing professionally, clearly the hacked V2 clone was never a good option. But for a hobbyist that was not sure about STM32 development, the V2 clone and a Blue Pill was the cheapest way to get into STM32 coding, for around $5 all included