The Dragon Balls that never was

[Kikoha Hater]

After Piccolo underwent his permanent fusion with Kami becoming the son of Katattsu, why couldn’t he create the Dragon Balls anymore? Was this something he could only do with his "evil" side expelled? Wasn't the son of Katattsu considered a Dragon-type prodigy as a small child, before he even became Kami?

[Bussani]

After Piccolo underwent his permanent fusion with Kami becoming the son of Katattsu, why couldn’t he create the Dragon Balls anymore? Was this something he could only do with his "evil" side expelled? Wasn't the son of Katattsu considered a Dragon-type prodigy as a small child, before he even became Kami?

If you consider GT canon, the son of Katattsu already created dragon balls, the dark star balls, which became active again when him and Kami fused.

If you ignore GT then I don't remember if they ever gave a reason... But Goku grabbed Dende pretty easily, so it all worked out.

[Casual Matt]

After Piccolo underwent his permanent fusion with Kami becoming the son of Katattsu, why couldn’t he create the Dragon Balls anymore? Was this something he could only do with his "evil" side expelled? Wasn't the son of Katattsu considered a Dragon-type prodigy as a small child, before he even became Kami?

The Son of Katattsu was indeed a Dragon Type, but when Piccolo Daimao reincarnated after his death at the hand of Son Goku, he became a Fighter Type. Since this reincarnated Piccolo was the base of the reuniting with Kami, he remained a Fighter Type thereafter, and ergo, did not possess the ability to create Dragon Balls.

[Dayspring]

Okay, here's my take:

-Son of Kattats (SOK for simplicity) = 1 Ryuzoku soul

-Kami = 1/2 (SOK) = 1/2 Ryuzoku soul

-Piccolo Daimao = 1/2 (SOK) = 1/2 Ryuzoku soul

-Piccolo Ma Junior = 1/2 (SOK) = 1/2 Warrior soul

-Nail = 1 Warrior soul

-Piccolo (Ma Junior + Nail) = 1/2 SOK + 2/2 Nail = 3/2 Warrior soul

-Piccolo (Kami + Ma Junior + Nail) = 1/2 SOK + 1/2 Nail = 1/4 Ryuzoku + 3/4 Warrior soul.

So it's because most of his soul isn't a Ryuzoku anymore that the newest Piccolo can't make the DBs. It's also why Piccolo says it's impossible to defuse as Kami + Piccolo (Ma Junior + Nail); the result would be Nail + SOK (Kami + Ma junior) instead. Even if he were to that, it may still not work as SOK is now only 1/2 Ryuzoku.