It's all spacing. His jumps happen to line up perfectly with platforms. Maximum height fulljump + dj lines up with DL and BF top platforms. Max height fulljump lines up with DL lower plat, and backwards fulljump will NIL (No-impact land), which also allows you to wL frames sooner. Backwards fulljump also will NIL on BF lower plats, allowing you to wL slightly sooner than the normal jump, which has to be timed precisely since the height of the plat doesn't line up perfectly with your jump height. But, Ganons dj at the ledge aligns you perfectly for wL onstage (ledgedash), and if you reverse ledgedash into a fp analog forward dj, you align perfectly with the lower plat for NIL or wL (pseudo dash). Ledgehop runoff to fp analog backwards jump will NIL on the lower plat as well, and all these apply to YS's ledge and lower plats too. Also if you wL, wd, or runoff the lower plat into fp dj you will NIL on the top plat (or wL obviously).
Wavelands are easier, input window-wise, when you fastfall, and Ganon's jump/fall animation means a lot. It's much easier to perfect wL from his neutral/forward dj animation than the neutral sh or fulljump, which is still easier than doing it out of a backwards jump. And EVEN HARDER (imo... might be a 1-frame input window non-fastfalled which is what I suspect for the backwards jump, which may be a 2-frame window for the wL) is perfect wL after a shield drop. The animation just isn't conducive to perfect wL and is arguably better to just angle the wL instead of going for a perfect one.