For many people it is a 'want' rather than a need. I posted in the 'regret or not' thread in this section about my experience with bikes. I can't do links yet. There are a lot of people I know paying much more than me for a bike, with some of them hitting 5 figures. I can't get where they are coming from at all. I have two £2000 bikes and some people think that is mad. People don't tend to start there though - they start at entry-level and then increase their reach / desire.
I have drifted in and out of photography. Had a minolta slr in the 80s. Started with cheap digital cameras to take photos of my children. Then used a Canon powershot, had several of them. I decided to upgrade and bought a Samsung camera with changeable lenses, which was all I needed. It had some surprisingly good low light performance, I like taking photos of flood-lit buildings and under street lighting and intended building on that. Then Samsung pulled out leaving me stranded. The cost of lenses went up, but I felt that was likely to be short-lived and didn't want to continue to invest in an obsolete system.
I then moved to a DSLR, an entry-level Nikon d3300. The sensor is the same as some of the higher spec DSLRs with fewer camera functions. I've had it for over 4 years. I have built up a desire to get something better and was looking at full-frame. I did my research and came to the conclusion that mirrorless was at a tipping point, and after my experience with Samsung I didn't want to be stranded again. I've just taken early retirement and my colleagues generously contributed towards a new camera, so I've bought a z5.
Do I need it? Not at all. I'm probably not a good enough photographer to justify the d3300. I wanted it however, can afford it and went for it.
I once read an article by a guy who gives financial advice to lottery winners. He said people's ambition is limited by their experience and what they know. If they live in a 3 bedroom semi and win big, they will buy a 4 bedroom detached because is where their ambitions are. They then move again. He said they all end up in the manor house, with a couple of acres and a duck pond, but some of them take 2 or even 3 moves to get there, because they cannot possibly imagine that for themselves.
I don't know if that is applicable to cameras or not, but it was interesting to me, how people were self-limiting, even when they had more money than they would ever need.