Colonisation is OVER

European countries have colonised and used Africa's land and people for some time, from the Portuguese to the British, and yet we've stopped trying to "take over" African countries.  Contemporary times seem to be focused on reparations or dealing with the consequences of colonisation, instead of continued use and exploitation of the land.  Why?  Is the land that shitty that agriculture won't continue to thrive?  Are the people that lazy that they can't force everyone to work towards industrialising civilization? 

Also, how can we terraform dry and arid land into fertile soil in order to grow crops?  This applies to Africa, the middle east, and parts of asia.  There is so much unused land, so why can't it be infused with nutrients, fertilizer, nitrates, etc.

That's a remarkably rosy way of seeing things. In reality businesses won't invest because of political instability, large amount of disease and violence, little education, and almost no infrastructure.

There is no point setting up shop if tomorrow the government claims everything belongs to them or the guerillas down the street decide bombing is fun, or if everyone is so sick they cannot work well, or (for some kinds of business) they aren't educated. And how are you supposed to do anything if the power grid is almost nonexistent and it takes two hours to place a phone call (true story)? Satellite is expensive.

Convincing governments is yet another matter. They already spend too much, hence their debts. If you want them to spend more, they'll need to jack up the taxes, and most citizens aren't interested in that. And what's the point investing with warlords and dictators pocketing everything?