Your CRX weighed less than half of what the current smallest car (save the Smart) does.
All those mandated safety requirements and gear add weight to the car. Airbags alone add about 500lbs to the structure of a car.
Weight is the enemy of fuel economy.
Your CRX is illegal to manufacture and sell today.
I did a little Googling and came up with:
2009 Ford Focus wt. = 2623 lbs.
2008 Honda Fit = 2512 lbs.
1985 Honda CRX HF = 1713 lbs.
So, “less than half” is a bit of a stretch, but, nonetheless, your point is well taken. All these nits who think the auto companies can just increase fuel economy at will are not taking all factors into account.