I'll answer : we could've had a left-wing coalition, but politicians are what they are, spineless guys who care more about their own than actually creating a revolution. There were several left wing candidates, one had 18%, another 6% in the polls. The second one refused to withdraw his candidature and join the one with 18%. He might have beaten Macron in the second round, and even if it didn't happen, the left would be far more powerful there in terms of opposition.

Besides this, you must understand there is a huge amount of abstention, and a lot of Frenchmen hate Macron, from anyone left and right of center, making it so french politics are extremely fractured. There's also the need to add France is a dying social-democracy, with problems in regards to religion and immigration. Polarization takes place, and you have an even more divided population, with huge support for either socialism or nationalism.