The current state of the game is also not favorable for such a long break without any updates. Massacre campaign is out and probably beaten by a good amount of veterans already, but Massacre survival is missing. Keep in mind that the game and especially the long term motivation in a DD game is mainly driven by loot. And there is no point to overgrind the current content, when all your gear will become obsolete with the next big update.
You could argue, that people might want to prepare for Massacre survival by gearing up, but exactly this gearing up process has already happened and was too fast. DD1 was extreme in this regard, maybe a bit too much, but that super lucky RNG drop was something, people could spend many many hours into. DDA is on the opposite end again, making it quite easy to get decent sets within a few runs. And - as I said - it is just not worth it to grind the last bit of stats out of the current content at the moment.
In addition the shift towards hero damage and the massive nerf of tower DPS might be harmful in the long run for Massacre survival. Frankly, the balance was fine for the campaign mode - I would even say that's how the campaign mode should be - more focused on hero damage / active gameplay. But I cannot see that work well with multiple, hour long survival runs. The focus on hero damage requires (too much) active gameplay and many players, who just like to set up a relaxed farm run might not play that much then. If you want to encourage high activity from the players you also have to reward them more. This shortens the gameplay time and therefor reduces the player numbers more quickly.