A friend of mine uses Sony APS-C because it is the smallest and lightest gear that does what he needs. Another one uses Nikon because he tried one out, liked the ergonomics, and changing systems when yours is perfectly fine is nonsensical. Another 'nother has Canon because her boss wanted his older gear to be used and loved, so he gave her a very good price*. I use Pentax because it was the cheapest way to get into photography with a well-built body and a wealth of cheap vintage lenses to play around with**.
For all of us, a change in the gear someone else used, an ebb in the Evilbay tide or Olympus having a good sale would have meant completely different gear.
And I'm sure we would not be particularly (un)happier
*I'm not getting into specifics, but I'm talking jaw-dropping, no-brainer cheap.
**Came for the price-quality ratio, stayed for the quality