Lower barrier to entry, all you need to get started are some photos. Creates a higher user population, so the % of creeps is lower (from conversation, this seems to be what turns my female friends off traditional dating apps)
And lastly, there's no real negative social stigma attached to it, partially because it's so popular. With traditional dating sites, people think you're a loser if you have a profile.
Heh, seriously. I know tons of couples who met on "traditional dating sites"; whereas if I found out someone I knew used tinder I would consider them pretty skeevy and would (metaphorically) inch away slowly.
I assume you're applying the same standard to people who met in a bar?
Really, this is entirely your problem. I've never used dating services or apps, but I've had several great long-term relationships which started in a variety of weird ways. That's just life, man.
And lastly, there's no real negative social stigma attached to it, partially because it's so popular. With traditional dating sites, people think you're a loser if you have a profile.