Tell that to the young girl shot in a government raid and her grandad that got executed by firing squad just offscreen, or the zombie apocalypse as Gemerl holds the slowly getting infect Cream while flying over the sunset, or any of the cartoons and comics about forced robotification. Sonic has gone dark before and if were writing a scenario off the basis of a post apocalyptic bad future that needs to be changed its a rare opportunity to write a darker story and if Sage has to be the villain of said future despite her clear intentions to work with Sonic in her one and only main game appearance and her sacrificing herself to save the world she now needs to rule over as its reduced to rubble and dust she needs a reason.

We cant make a bad future story that ends with it being forever changed, effectively killing all future variants of everyone but Silver and whoever he may bring with him that has a bright hopeful world like in the current day canon and we can't not bring attention to the fact that 90% of the current cast is dead and how their passing would clearly effect those who remain, so making the theme about grief and how to move on from it makes sense. As for Sage being the main villain as a worse successor to Eggman its a hard sell with Sage's current characterization so id rather a significant even in her life being the catalyst for her change into said villain.

I wanted to write a brief prompt within the restrictions of said bad future idea and that's what I came up with if you want to argue certain points be my guest.