-This is why there isn't a sequel to Cave Story
If there was a sequel to the game, Nicalis (please for the love of God use the right capitalization, everyone) would make it. It might be in works, who knows? But knowing how toxic this fandom can be when it comes to Nicalis, I don't think they would want to release it.
This is why we don't have Beta Cvae Story
No, it was Pixel's decision to not release the beta. He thought of it as too buggy, which is understandable. I wouldn't want to publish my old, buggy, and cringy software now either.
This is why Pixel avoids talking about Cave Story
Why would he talk about Cave Story (a 15 year old game) when he has published a newer game that he can talk about and promote? Especially considering the toxicity of the fandom.
Considering that
NiCALiS is literally hiding the fact that fans are pissed with them over the rights, I think it's pretty safe to say that at least some truth in these complaints. If the truth was different, I'm sure NiCALiS would come forward and say so.
As if that would matter anything to you. You and everyone else with a hateboner for Nicalis* would just say they're lying if they actually responded to the accusations. Hell. You'd even say Pixel was forced to lie about it if he responded instead of Nicalis. Like Cyber said, there's nothing wrong with hiding toxic replies.
Because legally, he might not own the rights to it
Nicalis owns the IP, but Pixel still has rights to it. It's literally how most video game publisher companies work.
Do you really think that if Pixel actually got tricked into signing a shady contract, nobody would have told him already? It's been years now since their partnership. Pixel still hangs out with Tyrone, still gets revenue from the Cave Story sales, and is still in a good terms with Nicalis. Do you really think he's not happy with his partnership? You're basically saying that Pixel is "too dumb to notice that he got fucked over by Nicalis". If you really care about Pixel, would you make this accusation even though he's clearly not angry with Tyrone/Nicalis and (like he mentioned) gets a percentage of the sales?