Sedans and coupes have gotten larger as SUV’s and 18 wheelers have become more and more common on the roads. They get bigger in part to fit safety features into the areas you can’t see. These cars get heavier because of government required (in the US and EU, anyways) safety systems like airbags, backup cameras and all of the wiring and other parts such systems require.
I don't believe for one moment that the HUD on a modern SUV requires all that space for its wires. It's a commodity computer connected to a commodity touchscreen. The airbag hasn't meaningfully changed in the last 25 years, either.
Cars have gotten larger for two primary reasons: larger crumple zones (a legitimate safety change!), and to circumvent emissions regulations. Of those, the latter has been a much stronger pressure.
Commodity computers and touchscreens weren’t in many cars 15-20 years ago. Cars with features like seat cooling and heating were premium trim level versions, now those are more widespread. Wiring for cameras? Wiring for lidar, radar, and all sorts of other sensors? The sensors (and presumably their required computer system) themselves? All add weight. Also, using steel as opposed to advanced, lighter and more expensive materials, the larger crumple zones (safety features) weigh more.
Side air bags have increased in popularity in the last 25 years. Although it looks like they reached 100% in 2012, so presence of side air bags doesn't explain changes in the last 10 years.
