Why is it taking so long for humans to be taken to Mars ? Also to colonize Mars .?

We have the technology to do it . If you read Robert Zubrin's the Case for Mars, he already present scientific ways of getting ppl to Mars cheap and building what we need there with only minimal supplies from Earth, not having to send all the supplies from Earth to Mars . Also this is about the survival of our species because as history as shown, nothing lasts forever, not even Humans if we're confined to just one planet . That we should settle other worlds . You never know . We could be hit by an asteroid or global warming . So many scenarios . My question is why isnt the nations of the world taking a more active role in this ? We have the technology now, we have the money and we have the ideas that seem more than plausible . What else could there be ?