DP headcanon (I haven鈥檛 done this in a long time). What if it鈥檚 easier for Danny to be Phantom so he stays like that for as long as he can. Like, transforming back into a human and staying that way for long periods of time takes more energy out of him.
I feel like you see that a lot more in the first season, especially in Mystery Meat. I dunno. I鈥檓 probably not adding anything new. 馃槄