Well, as far as I know, there are 3 PRIMARY issues that made Mars the way it is, today:
1)
Firstly, Mars is simply TOO SMALL and TOO TINY, compared with Earth.
Put it this way: if Mars was a human male, he would drive a Hum-V in order to compensate.
Because Mars has so much less mass than Earth, it ONLY has about 38 percent of Earth's gravity.
That kind of low gravitational field, literally means that if you brought cats and dogs to Mars, to live under that future dome with you, they would literally be able to leap and bound pretty high into the air, OVER your head.
Good luck catching Sparky and Mittens if they run loose beneath the dome.
Such low gravity, also means, some scientists suspect, that you could have a real increased chance of drowning in a swimming pool, simply through normal movement and splashing about, which would create much higher amplified wave resonance in swimming pools, under such low gravity.
I guess the "fat kid" doing his trade mark Cannonball off the high dive, would in fact create a mini tsunami in the Martian recreation gym.
All of this is to say that with such a weak gravitational field, Mars really could NOT hold onto a thick, warming, loving atmosphere for life to thrive very long at the surface. The atmosphere just simply got whisked away by the solar wind.
2)
Another major factor, also related to size, is that Mars' interior cooled MUCH faster than Earth.
Here on Earth it takes spinning liquid iron to generate a magnetic shield.
Yup that's right: the planet Earth has a giant Star-Trek like, invisible force field, that envelopes the planet with a magnetic field, and whisks away, and redirects all those high energy charged particles and radioactivity beaming down upon us from the sun.
So... ideally it's nice to have a giant invisible shield around your planet! Mars lost it's giant Star Trek shield, probably a couple of billions of years ago.
3)
FINALLY... the other major issue: Mars is VERY FAR from the basking warmth of the sun.
People often just don't appreciate how truly further from the sun Mars is.
That means DRAMATICALLY less warming heat energy. A LOT less.
SIDE NOTE:
There are also a lot of other more "smaller" issues that Mars has going against it... such as the lack of a large moon, to generate tides for life to colonize land, and also the stabilizing effects a large moon brings to a planet's rotational wobbling... etc...
But suffice to say, Mars could not evolve thriving, tropical, lush jungles with dinosaurs.
But... it may still have evolved life in the past, and that life could still be thriving today underground, in possible vast underground great-lakes. Maybe.
As well.. it's worth noting that humans can change Mars.
For example: we already know how to warm an entire planet! We seem to be experts at that! (ie: global warming)
There are some known HIGHLY potent greenhouse gases that we know of, which could theoretically warm Mars SIGNIFICANTLY within only 100 to 150 years. So we would have to establish several many factories, to constantly pump out those global warming gases, and begin to thaw out the planet.
In addition, an orbiting series of mirrors would also significantly increase the amount of sunlight/heat hitting Mars.
Thus, Mars might not be the way it is, for very much longer, if humans have a say in the issue of that planet's future.
