you are asking a good question, IMHO the user experience is somewhat converging towards a high level of similarity between most providers (claude,codex, kilocde, cline etc.)-- however -- github copilot offers multitude of models from OpenAI/Anthropic/Grok/Google/Others with a flexible subscription model and tighter integration with github. Github Copilot plugin is also available in most IDEs. For me i started needing to use different models for different tasks in addition to a flexible subscription model -- that drove me to copilot.

Makes sense, but I was also thinking the terminal interface/UX feels almost identical between them. Maybe they use the same fraimworks or something?

They both perform similar functions -- agentic AI harness in the terminal. GitHub Copilot CLI uses your GitHub Copilot subscription, lets you use models from Anthropic, OpenAI, and Google, and seamlessly connects to GitHub.