I'm sure that part of it has to do with the art style. Not to undermine just how high quality the storytelling is, but it helps a lot that it just looks so different. You can't look at Ping Pong and think "oh, it's just another sports anime." So you get a really good first impression right off the bat.
But yeah, its character driven narrative is far more varied, with a lot of strong and visible development. Most sport series revolve around constantly high levels of testosterone (and that specific "sports" kind of testosterone too). Granted, sports series have gotten a lot of quality out of it, but it presumes a greater interest in that type of show too. And a lot of times, for those that aren't already interested in that backdrop (letting them enjoy the more subtle differences), it leads to a lot of sports series that all feel identical to one another.
Naturally, Ping Pong slides past all that by doing its own thing, and being about the sport as little as possible. Hell, the amount of time they focus on actual Ping Pong could lead you to say that it shouldn't even be considered a sports anime.
Another sports series I can recommend to typically non-sports anime fans is Chihayafuru. It still has some of those typical sports anime idiosyncrasies to more limited degrees, but it's strong focus on characters and varied motivations makes it stand out. The chemistry between the characters is its best feature. It's the reigning champion of "those little moments," lol