I'm surprised that even nowadays there isn't a way to port styles over to some kind of universal system within WordPress to avoid this issue. I think it stems from the fact that developers/brands want you locked in (purposefully) to keep using their products.

I can understand why, however it creates a lot of trouble for site owners to migrate to different themes and plugins over time which does hold back the community in improving their sites. I don't think there's an easy answer to this, but hopefully a solution can be thought of.