Short version: Illustrator is a tool focusing on vector graphics. Figma is a tool that focuses on collaborative interface creation. Both of them are good in general, but depending on your needs, one could be better at that.
If you work in a large company where you need to maintain Design Systems and you frequently collaborate across teams (think different OSes), Figma would be more helpful for everyone. Especially because it has specific features to make that work good.
While if you're a lone designer doing design for physical products, you're probably better off with battle-tested Illustrator that has a lot more functionality around manipulating vectors.
In the end, it all depends on what you're doing. They have different use cases they want to cater to the best.
If you work in a large company where you need to maintain Design Systems and you frequently collaborate across teams (think different OSes), Figma would be more helpful for everyone. Especially because it has specific features to make that work good.
While if you're a lone designer doing design for physical products, you're probably better off with battle-tested Illustrator that has a lot more functionality around manipulating vectors.
In the end, it all depends on what you're doing. They have different use cases they want to cater to the best.