I don't doubt* that larvesta and charcadet will be made more accessible in some future event, it's just that of all the nonsense Niantic does, egg events are particularly egregious. Except for the hatch days when the spotlight mon is literally the only thing in eggs, egg events are just never worth it. I have hatched one (1) larvesta since release, and as far I can tell there isn't going to be any significant boost to it or charcadet's hatch rates, so I have no incentive to spend coins on incubators just to get the same results I've been getting for months. For the folks aiming for shiny slugma or litleo maybe it will turn out to be worth it for them, but Niantic is definitely counting on whales to go hard on trying to hatch shiny larvesta. And to top it off, there aren't even any event spawns!
*Ok, I have some doubt. It's been 2 years since salandit was released and I don't think there's been any event to make it (particularly female salandit) more accessible, even despite varoom being the fancy new addition to the 12k egg pool.