Photography has changed, evolved and progressed over the years. As a professional photographer, there was a time when I owned 3 lenses for three different cameras. I shot press assignments and weddings with a 4x5 press that camera equipped with a 135mm lens. Well, I did have a spare camera in case of a malfunction but the lens was identical. I walked in close for closeups and stepped back for wide shots-SIMPLE! For commercial work, my 4x4 view camera had a 240mm lens to accommodate swings, tilts and shifts. For portraits, in the studio, my 5x7 camera had a 300mm Tailor, Hobson, and Cooke variable soft-focus lens! That was it!
Over the decades, formats, cameras, styles and customer demands all changed. Medium format and 35mm systems, came into more frequent and popular use in professional by advanced amateur photographers. Each system accommodates a vast array of interchangeable lenses. Nowadays, of course, full-frame and medium format digital cameras are the tools of choice among advanced workers and pros and of course, there are a plethora of lenses on the market and more being designed, manufactured and introduced all the time.
So...why HAVE all those lenses? If a photographer confines themself to one kind of work, three lenses or even less may accommodate all of their needs. A normal, medium-wide range and moderate telephoto focal lengths may do the trick or perhaps a few zooms that cover that range. A kit like this will accommodate landscape, some portraiture or people photography, maybe some sports or activities, and whatever. Suppose, however, you want to do some serious architectural or interior shooting maybe a perspective control lens would be in order or a super-wide for confined spaces. Maybe a macro for exceptionally sharp bugs and flowers.
Serious sports or wildlife shooting is your game? Tou can't walk or on a football field, a race track or a soccer pitch during a game or a race! Birds, ferocious wild animals? Time for a super-telephoto model. Have to shoot a black cat in a coal mine at midnight or get some exceptional cool "bokeh"? You may need a very fast lens- a nicef/1.0 or even a bizarre f/9.5? Big Bucks!
Remember too. different focal lengths don't only make things look closer or further away- they enable you to work at different distances and distance influences perspective. You can preserve, compress, expand perspective for creative purposes.
I guess you are getting the point by now. So, these are someof the practical and technical reasons for owning multiple lenses. Professional or avid travel shooters want to have some redundancy or overlapping glass in the event of a breakdown in the middle of an assignment or a trip. Then there are psychological reasons as well.
As you mentioned, some folks are obsessive and want to have every lens in existence- whether they need them or not. If they can afford that, why not? Everyone should enjoy their photography however they please! A more frugal or practical photograher may mock them and call them "gear-heads" which is actually a crank-operated tripod head.
Many years ago, Modern Photography Magazine published an article entitled "Are All Photographers Nuts"?! I found it very humorous. There was one psychologist that related long lenses to voyeurism and opined that some guys see them as a phallic symbol like sports cars with small cramped passenger compartments and extremely long engine compartments. Some photographers love extremely long telephoto lenses or superwide with enormous front elements just to impress other photographers. Different strokes!
Photography has changed, evolved and progressed ov... (