This could be limitations of the artist and of the medium. These images were produced by chromolithography, a many-staged process of chemical interactions. Add

This could be limitations of the artist and of the medium. These images were produced by chromolithography, a many-staged process of chemical interactions. Adding lots and lots of details and tiny, realistic figures would be difficult. And perhaps expensive. I can imagine a situation where the cost of the process is an exponential function of the number of places different colours have to border each other without bleeding. It's tricky enough to draw that kind of thing in any medium.