Mars Barred
On what type of timeframe were you imagining that the shoebox of lichen you send to Mars was going to transform Frozen Airless Radioactive Desert Hell into a place where people could grow wheat?
People have this idea that life is like some kind of magical force; that the reason Mars does not have life is that life has not yet gone there; that once life goes to a place, then it just figures out how to go on living there. This, I think, is a consequence of more people having gotten their science education from the movie character Ian Malcolm than from actual science classes. More generously, it is a testament to humans having formulated nearly all of their ideas about the nature of life from the absolute easiest (and only known) place to have life.
Source: Neither Elon Musk Nor Anybody Else Will Ever Colonize Mars
And The Mars crisis, explained by 2 experts covers even more reasons that we’re not going to Mars (from the writers of Saturday Morning Breakfast Cereal Comics).