OP could just compare the E30 3-series and the G20 3-series and there would already be a size difference. Of course, much of it stems from safety features taking up extra space (hello crumple zones, airbags, etc) and there’s also simply a little bit of more space in a modern car.
To truly make a point here, you might want to compare a pickup truck from the 80s or 90s vs the 2010s or 2020s. Those have gotten unnecessarily big with no excuse.