I sell things I don't use, so I only own 3 keyboards.
Why own something you aren't going to use and enjoy? I don't understand that collector compulsion. People do the same thing with game collecting, buy hundreds of rare games and never play any of them. Why?
I feel there are a few very generalised reasons; they in fact do use all of their stuff, combined with wanting/hoping that the value keeps, perhaps there's a great sentiment involved, or they are in fact are unhealthily obsessed. But I'm not qualified in the slightest to be able to make an absolute determination.
If you're interested to know my take on my collecting habits to see how one might rationalise it. I rotate between most of my keyboards in roughly a three-day basis to mix up my experience - as someone who works in front of a computer (programming) and relaxes in front of a computer (usually writing stuff), I feel it helps makes those mundane or precise tasks (respectively) just a little more interesting and it would be awkward to have to sell and buy keyboards every three days to fulfil that desire. And I know I've mostly got IBM buckling springs stuff that's very closely related, but a lot of the individual keyboards have slightly differing sound characteristics and/or unique layouts and/or features to play with. And secondly, a lot of my older stuff keeps in value and is something I can use and enjoy every day and liquidate when times get tough despite allowing me to enjoy that a self-aware shopping 'high'. Thirdly, I feel like it helps me connect/own a little bit of history from the industry I'm involved with and care about. I, of course, cannot outright rule out unhealthy elements to this that might exist subconsciously, nor am I a psychologist that could properly analyze and diagnose this, but I believe I've managed my enthusiasm well enough that I'm not distracted from my work or completely bled my wallet and my very student spending limits. In summary, clearly I'm indulging in indulgence, but it's mutually beneficial for enjoying parts of my life.