Instead, parts of our atmosphere act as an insulating blanket of just the right thickness, trapping sufficient solar energy to keep the global average temperature in a pleasant range. The Martian blanket is too thin, and the Venusian blanket is way too thick! The 'blanket' here is a collection of atmospheric gases called 'greenhouse gases' based on the idea that the gases also 'trap' heat like the glass walls of a greenhouse do.
From elsewhere on their site:
Venus - average distance from Sun 67 million miles
Earth - average distance from Sun 93 million miles
Mars - average distance from Sun 226 million miles
As the intensity of light received from an object is inversely proportional to the square of the distance, it'd be reasonable to expect the Sun's rays on Venus to be 193% as intensive as on Earth, and on Mars to be only be 17% as intensive on Earth. Which might have something to do with the temperature differences.
I can't argue with that!