This comes as no surprise to most, because when Google launched Bard (the name Google used for Gemini early on), Google said it would bring Bard features to the Google Assistant.

Google announced Assistant’s phase-out, upgrading devices to Gemini with Android 10+ and 2GB RAM minimum requirements.

The time has come for the Google Assistant to be replaced by Gemini, Google's younger and better assistant (despite it being wrong way too often). Google announced, "Over the coming months, we’re upgrading more users on mobile devices from Google Assistant to Gemini;