Why DSLR?

You're (purposely) confusing snapshots for keepsakes and albums with professionals, hobbyists and enthusiasts taking photos to develop their technique and skill using a complex medium (a DSLR or similar grade camera).

To put it simply, a 'whole purpose' for you does not at all apply to everyone...The same way veteran model train hobbyists cannot be compared to a parent setting up a set for their child under the xmas tree. The former can elevate miniature work to an art form with an eye for detail honed by decades of work, while the latter is doing something fun and traditional.

Neither is wrong, but one is very different from the other. Either way, you shouldn't need someone to spell out what's compelling about a hobby or profession to show basic respect rather than questioning people's investment as 'blah blah blah' frivolous or less 'useful'.