That's because it's the same prop saber throughout that scene.
In the context of the movie, while you do see the saber quite a bit in the Finn scene it's never shown in a close-up, so it didn't need to be a Hero saber.
The Maz saber is the Hero, and filmed inside the studio. Those Finn scenes were filmed at a different time outside on location and the Hero prop saber was not used.
First, sorry for the multiple posts instead of combining my responses into one. Running in and out of my office. No time to get them all done at once.
I'm gonna have to disagree on the grips-to-bottom saber not being a hero because "it's never shown in a closeup..." The scene of the saber being taken from Finn's hand is zoomed in on his forearm. The scene of Finn reclaiming it from the hand of the fallen trooper is again zoomed in on the saber. The scene of the saber stuck in the snow is zoomed in on the saber. IMHO, each one of these shots is zoomed in enough to warrant referring to them as close-ups.
Now are they "close-ups" to the extent that the Maz saber gets a close-up? I would definitely agree that they are not. The Maz saber doesn't just get a close-up, it gets a LINGERING, TIGHT close-up. But the quality/length/extreme tightness of the Maz saber closeup doesn't, again to me, negate calling the shots of the Finn/Snow saber close-ups.
Also consider that in each of the close shots of the Finn/Snow saber, a saber with GOOD examples of every known feature appears (genuine and CLEAN Graflex body, straight, unbroken/unchipped grips, the clamp cover to conceal the Graflex branding, evenly-cut notches for the rivets/screws, a red button, a glass eye (even if the knurling is turned down), etc. It does not give the appearance of a saber that is missing one or more key features, or was given any less attention construction-wise than the Maz chest saber.
The attention to detail, along with the fact that it is indeed (in my opinion) viewed in several close shots makes it hard for me to group it in with an FX saber that has an obvious antenna sticking out the bottom, or one with trimmed grips with no rivets and cloth/rubber construction. Those to me are stunts, and the Finn/Snow saber just doesn't seem to belong in that same category.
It's an outdoor hero, which we also see in close-up.
My thoughts exactly! Outdoor hero, action hero, Finn/Rey hero (vs. Maz/Chest hero)—whatever we want to call it—but I think of it as a second hero.