They are ordered wholesale and also consumed in bulk.
For each order, the production costs are optimized, and the appropriate technique and type of printing is selected. Graphic designers, DTP operators and printers deal with this.They are responsible for the quality of the printout and as soon as something is wrong they are the first to be targeted by the dissatisfied boss. Their work is quite hard and I have to admit that you have to really have a fuss to do it. Work after hours, maximum focus and responsibility - definitely not work for everyone.
That's why certain standards apply. In polygraphy and graphics, such standards also exist - appropriate definitions of CMYK colors - key for the appropriate color reproduction.Specified in advance formats for printing leaflets and business cards, so that they are comfortable and as uniform as possible.
Without standards, even leaflets could be completely unreadable and even repulsive. .