Like Jack's point #1, the way we communicate our ideas is such an important facet in team collaboration. And when the conversation is about process/workflow/tooling, people can be fairly protective. A thought that comes to mind is taking one of the creatives you guys have done, or a small piece of a previous/current project, and re-animating what was previously done with CSS with GSAP - do that on your time. Maybe showing them a working example that they don't have to put any effort or time into can help bridge any communication issues, or be something that is a gentle nudge now, but helps moving the ball closer to GSAP integration in future projects. Good luck!