As has been mentioned above, the default templates use very simple styling, to make it easier for people not familiar with HTML/CSS to modify the basics like font size and color. I took a brief peek at your first template, and while you’ve tried to keep things simple, it still has about 5x the amount of CSS, which I think is going to be a fair bit more daunting for people not familiar with it.
One possible way we could work around this is to make some of the styling implicit and not explicitly shown in the template. But doing so would make it harder to discover the things that had been tweaked, and has the potential to cause disruption to existing card templates.