Ok, baryta (barium sulfate) is commonly available in many forms from many sources. It is used as a 'milkshake' and 'enema' before CAT scans and X-Rays to enhance images.
It is also coated in gelatin on inert paper to produce FB baryta photo papers. This process once involved adding tints and is no longer done. Baryta paper is probably produced by only 3 companies world wide do to the need for a complex process called calendaring which can be "hot press" or "cold press". In this process, the paper + baryta is compressed into a smooth mass with the desired surface such as glossy, rough, matte, silk (no more) and others.
At the present time, baryta production has been undergoing a rather rapid decline since the advent of digital due to the fact that digital inks generally don't like to go onto the baryta type papers. They need a new type of surface. So, most of these companies want to get out of something that "no one wants anymore". That comes from a major producer of baryta paper BTW.
So, WW production is down to about 20% or less of what it once was, and is still declining. As it declines, the machinery to produce the paper is scrapped. So, buying FB paper is not going to solve the problem if companies like Ilford just cannot buy the paper from their source anymore.
It consumes more water in manufacture, and it consumes more water in processing, therefore it is becoming less attractive to all phases of analog print production.
Oh, to answer some other comments, it lies beneath the emulsion layer and increases the reflectivity and sharpness of the photograph (depending on surface). It whitens but does not brighten unless brighteners are added. It offers no significant protection to the emulsion itself, and if manufactured improperly can even degrade the integrety of the image by becoming brittle and flaking off. This can result if the baryta is not made with the right proportion of gelatin, humectants and hardners, or if it is not calendered properly with the right heat and pressure.
PE