I joined Era through GAF, so the more interesting question is why GAF:
I came to GAF late--in 2015, despite having been gaming since the 90s. Generally, I did not use the internet much.
Overtime my hobby dwindled: I have generally conservative buying habits and the HD revolution killed so much of traditional stationary console gaming for me, outside of Nintendo. Then Federation Force happens and I become incredibly frustrated and despondent with gaming. I start commenting in comment sections, which, are well, a cess pool. I start seeking out boards. That leads me to GAF.
GAF reinvigorated my gaming hobby. For as cynical, hyperbolic, and just plain toxic we can all be there is a lot of good information and recommendations about games hidden underneath. I opened myself up to gaming suggestions and exploration and my gaming life has subsequently much improved.
I don't really use Era in the same way though. I found a community at the tail-end of GAF/beginning of Era and I've mostly sequestered myself in said community--increasingly so. Get a lot of good recommendations and deeper cuts that way without all the other stuff. Plus camaraderie.
IDK. I've been trying to reengage with broader Era again since the anniversary. It hasn't gone particularly well :P (which is on both me and my expectations but also honestly on Era). Still, I believe in the place on some level and the community at large has a certain place in my heart.