The United States and the West have always outsourced security provision in North and West Africa to the French, since they were the colonial power there, including in Mali, and have the best ties and expertise.
As to why it makes sense for the West, especially Spain, to support France in Mali, even if allies should point out what they think is important, like dealing with the Tuaregs in some pacifying fashion, Mali itself from a resource point of view currently matters mainly because of Gold, as to how they pay their bills.
That's not in itself anymore important than the proverbial price of tea in China.
However, Mali is how the uranium of Niger gets to market, and that matters rather a great deal from a security point of view.
Remember the whole Scooter Libby affair, about the "yellowcake" uranium Saddam allegedly wanted?
Now the story itself wasn't true, as the "Italian Memo" was a forgery, curious as to its origins unknown, and it never made too much sense, as Saddam already had a enough yellowcake for his purposes, but the broader point remains, that Niger is a major source of uranium ore, one that one doesn't want controlled by just anyone.
That's because if the yellowcake ore ultimately produced in Niger by the French corporation Arreva in Western Niger isn't in itself particularly dangerous, as to "dirty bombs," those facilities are on the edge of Mali, and populated by a people known as the Tuaregs, who are a bit of a problem lately, if in a difficult spot too.
Again, you don't want just anyone buying uranium ore as to Niger mattering because to get to anyone at reasonable cost, it's by far easiest to go from the mines in Western Niger through Mali.
As to the Tuareg issue, and why the use of force by France it makes sense to support needing to have a diplomatic context, the Tuaregs are a nomadic people who have run into the French before.
It's not easy being a nomad in the modern world, because as with the Bedouin, the traditional lifestyle sits uneasily with States having frontiers, especially with the Tuaregs as to the desertification issue making resources more scarce in many instances, and because of course being a nomad lends itself to being a smuggler, as with drugs, or as it would with Uranium, the latter as to why care and therefore support France in Mali.
The current situation in fact of Islamists taking over northern Mali in no small measure was created by the difficulties of the Tuaregs.
Basicallly, a lot of Tuaregs didn't have a lot going on, which combined poorly with Qadhafi having a lot of money and big ambitions in the region, and a need to police his own dictatorship.
Outsiders have often been popular in such circumstances, as they have no existence in the host state save at the suffrance of the current ruling class.
Thus, when Qadhafi fell, one issue that predictably emerged was a lot of unemployed, and unwelcome, Tuareg mercenaries, who of course might as well have grabbed a lot of weapons before the bullet hit them in the head on the way out the door. A lot of Libyans had come to not like the Tuaregs, still a problem, because the Libyan part of the Tuareg issue isn't over in Fezzan of southwest Libya, notable as to where the Al Qaeda attack on the Algerian gas refinery started.
So, lots of unemployed mercenaries of Tuareg background leave Libya after Qadhafi is shoved out, and one place to go is Mali.
That was the origin of the revolt there, which led to a coup in Mali, because the younger officers didn't like what they saw as a weak response, and then you get the real Islamists liking that situation, which of course concerned France for good reason, the one we care about the most being access to the Uranium mines of Niger.
That means it is wise to support France, not wanting the uranium of Niger to fall to just anyone, even as it is important to see that it's hardly just a matter of Al Qaeda either, especially with the nomadic Tuaregs, who can be difficult to deal with in a modern context, because their way of life as nomads is just a lot different than the modern context, if it would also seem that they like things modern too, as to why they kidnapped French workers in Niger too, wanting more from the uranium mines, uranium being a good reason to wish the French well in Mali.