Sakurai never said it was because of technical problems. He didn't say why he was rejected, but I highly doubt it wasn't because it was difficult to make him work.
In all likelihood, Sakurai probably realized that the odds of Sukapon ever appearing in another game again are extremely low, and that he was just going to keep getting more and more obscure. At the time that Sukapon did well on the SSB polls, his game was 6 years old. Now, it's about 14 years old and Sukapon has not made an appearance of any kind since Joy Mech Fight on the Famicom. No sequels, no ports, no cameos, nothing. It doesn't sound like we'll even be seeing him on the VC anytime soon.
The tone of Sakurai's response to the people saying they wanted Sukapon is like "Well nothing is technically impossible, but seriously don't get your hopes up". It really sounds like there's no hope for Sukapon from the way Sakurai says it.
There's nothing wrong with wanting Sukapon, but at the very least you can be more realistic about his chances and a little bit more understanding as to why people may not want him in. I'm rather neutral towards his inclusion, but based on the facts, I don't expect him in the least.