Why some black and white film require color development process

Question

For example, Ilford XP2 noted C41 on the box instead of d96 or d76, Kodak Black and White even explicitly warned the user "Do not process in B&W chemistry" on the film roll.

Why do these black-and-white films need the color process?

Edit: as pointed out by the comment, the name can be a bit confusing. Kodak Black and White is the literal name of the film I was referring to, not all black and white films by Kodak.

Below: Kodak Black and White film, the text PROCESS C41 ONLY can be seen on the box.

Answer 1

In the heyday of film photography – let's say the 1990s – C-41 film development was available everywhere. For the vast majority of people, photography meant taking photos on cheap colour film and dropping the film off at a convenient local photo processor – often getting it developed and printed in less than an hour. Traditional black & white development was the domain of only certain enthusiasts, and way too much hassle for most people.

However, casual photographers were still interested in the look of black & white photography, for the tone/mood/character of the results. Wouldn't it be great if there were black & white film available that could be dropped off at the same convenient local 1-hour lab and developed/printed in the same way as all the rest of the colour film around? Exactly – that's why these chromogenic black & white films were invented and brought to market, and why they still exist now.

I remember Kodak had a popular one called T400CN, and there was another using the Portra branding – I guess this one was particularly marketed at wedding photographers, allowing them to easily incorporate some B&W variety into their usual C-41 workflow. I guess Ilford's XP2 Super is the only one currently in production.

Addendum: To be honest, these films must not have been necessary at all if the goal was to get B&W results through the C-41 process – at least not in the latter days of film's heyday – because I did once drop a roll of colour film off for developing/printing and received B&W prints back. I obviously pointed out to the lab that these prints should have been in colour. They reprinted the photos in colour, and I kept the B&W prints too, which actually were quite nice in their own right. So it must have been possible for the lab to simply "flick a switch" to specify that the prints should be printed in B&W. I guess they might have taken advantage of this facility to avoid any colour cast in prints, which I remember sometimes happened with chromogenic B&W.

Answer 2

Initially photographers were also the darkroom workers developing their films and fabricating the finished prints. As the camera became more manageable, laypeople became photographers. These amateur photographers entrusted developing and printing to photofinishers. These became highly mechanized shops common in every metropolis. These shops eventually processed black & white and color films.

Then came the one-hour shop that processed and printed in the neighborhood. The cost to equip a one-hour shop was high and likely floor space limited so these shops specialized to just handle color negative film leaving black & white and slide film to the wholesale photofinishers.

In an effort to expand the business of these one-hour shops, black & white films developable in color negative film processes were devised. Like their color film counterparts, these films contain dyes that blossom and become full blown in the color negative developing machine.

In other words, the small one-hour shop only capable of color negative film developing and printing, could now offer black & white service if the photographer used this special film type.

Let me add, ordinary black & white films are not compatible with the chemistry of color film developing and XP2 and is not compatible with the chemistry of the black & white process.