Because I have it. I used to use my small one. But now that I have the one with the long handle, I use it. I find it works better than either my small tamper, or the flat "spade" that is on the back side of a pair of tweezers. If I didn't have one, I would use either of those. I mean, I went without one for years. But now that I have one, I use it.
A couple of reasons the long one works well. First, it reaches across the pot. But I work on a turn table, so that's not really a big deal. The attribute I like about it the most is that you can slip it under low branches easily. My old trowel had a handle, and the trowel part dropped down at one end. So, to use it, I have to be able to get my hand over the soil and push down. With this contraption, the long metal extension can get under there easily, yet my hand is away from the pot and any low branches. It's a minor thing. But it works really well. I agree it looks rather silly. The way Boon uses it, it's a gentle tapping of the surface of the soil. Kind of like the way a conductor taps his wand on the music stand. Easier to do with the long extension.
One potting procedure that Boon teaches that I think is really helpful, is tapping the pot to settle the soil after chopsticking. It's amazing how well that works.