The internet is like a highway. Simplistically, one route might take you to Virginia. Another route takes you to Texas, etc etc. And along the way, your route takes you through Ohio which has a major pile up at rush hour. Or you can think of it as McDonald's on the east end of town has a traffic jam so it's easier to get to Subway on the west end of town. A lot depends on where the servers are physically located, their networks, etc. (Yes pedants, I know it's more complicated than that but I said simplistically for a reason).
If SWTOR is in Virginia and WoW is in Texas, complaining that WoW works doesn't mean anything for SWTOR, You see? So using ping plotter you can find where the hangup is and call your ISP. You tell them where you're trying to go, where the traffic jam is and see if they can help you. They can reroute you a different path or get in touch with the area that has the problem. If they feel like it anyway.