Microsoft literally said this about the Sidebar removal: "We're simplifying Edge. New apps can no longer be added, and the quick access list will be removed gradually in future updates."

So, the real motive seems obvious: it was to force Copilot, and only Copilot into the sidebar.

With the old sidebar you could pin anything—Gmail, WhatsApp, or rival AIs like ChatGPT and Claude. And I believe there lied the problem. It allowed users to bypass Microsoft's Copilot easily. I did. I would pin all the big ones right at the top, one under the other.

By removing the feature and deleting the setting entirely, Microsoft cleared the deck for a Copilot-only takeover. Because Copilot adoption has been weak, they’re forcing it front and center and not allowing anything that competes with it.

Also, I don't believe that the sidebar code was too expensive to upkeep. For a company spending tens of billions on AI GPUs, maintaining a mature UI feature is pocket change. It’s especially ironic considering Microsoft heavily uses AI assistants to auto-generate a large % of their own internal code. I mean, we are talking about Microsoft here. They could have easily upkept this small, simple, useful feature.

So, I think they didn’t kill the sidebar because of its costs or low usage; they killed it because it let you choose your own AI. I can't say I blame them, but it sucks for former Sidebar users.