Why are there so many varieties in chemistry?

Because chemistry is too big a subject for any one person to know all of. So people specialize in one part of chemistry, usually the part that interests them the most.

Someone who studies the chemistry of petroleum products might have little need to know about the chemistry that goes on in interstellar nebulae, or the chemistry of snail mucus. A person studying DNA to find cures for cancer might not want to take time out to learn about how to make a better rubber band.

Specializing allows someone to concentrate on one area of chemistry, and one set of chemical techniques that are important in that area. A molecular biologist has less need of a spectroscope than an astrochemist would, and an explosives chemist would have no use for a DNA sequencer.

Theoretical and quantum chemists might not need any equipment at all, other than paper, pencil, and perhaps (these days) a computer. But industrial chemists might spend a lot of time designing chemical equipment to make things more efficiently or more safely.