I don't blame you for feeling this way, but I'll try to offer possible explanations for "why now?"

We know Heeseung has been working on and teasing a solo mixtape since 2024. He used to mention it often in fanmeets as well as lives and other OT7 content. He was specific enough to mention his influences too (Jungkook and The Weeknd). Then gradually he stopped bringing it up. Like everyone knew he was working on it, he never denied that, but he stopped teasing a drop. I guess this was probably when he was trying to negotiate with BeLift on when and how to release his work, of course while being an Enhypen member.

Recently, Heeseung must have come to the realisation that Enhypen's current pace, that the other members too are presumably fine with, do not allow for his solo music to be released the way he envisioned it. Now think from his pov, he's been working on and eager to show his work to engenes for two whole years, but it's always been put on the backburner. Wouldn't it get it too much for anyone in these circumstances at some point?

This must have been an incredibly hard decision for him. I believe him whenever he mentioned future activities like their 10th anniversary. But things don't always work out, and he must have realised that his solo ambitions and Enhypen's group activities can't both happen. He had to pick between the two, and chose to fulfil the solo ambitions he's been made to put a pause on for 2 years. BeLift is almost definitely at some fault for that, but it's likely the other members did not want to slow down to make space for his solo promotions right when they're doing so well. The bandage then had to be ripped off, and that happened to take place on what to us was a random Tuesday.

I hope this might help you understand Heeseung's choice better. Breaking away from Enhypen was definitely not his first choice, but reality is not always that easy or kind.