For example, in Libya, fighting on the ground was done by local allies, while intervening states participated in the conflict via relatively safe air support operations and by providing weapons to the local allies. Why this is happening?
I'm fully in sympathy with the travails and other difficulties of all oppressed peoples fighting to throw off their repressive overlords ... but it still has to be said that those oppressed people are the ones who will, in the end, benefit the most by the overthrow of their oppressors ... so, as unfortunate as it turns out to be, it stands to reason that, in all fairness, they should also bear the lion's share of the burden of getting rid of those they *allowed* to come to power in the first place.
I apologize in advance if I've offended anyone by suggesting that they actively assisted in this coming-to-power -- that's not my intent. It's simply to say that "It happened on your watch; you *have* to take some kind of responsibility for it having happened, even if that responsibility was laid on you by your parents actions or non-actions, or your grandparents ... it's still, in some respect, *yours*, and you need to be in the frontlines of dealing with it".
There will be others standing with you, certainly -- not *all* Westerners are satisfied with just supporting airstrikes and aid ... if you look hard enough you will see them also fighting and dying beside you, Westerners have a long history of taking up others' issues and bleeding for them ... it simply isn't *required* of them all, they *choose* to, when they do.
Their *governments*, on the other hand, make their support-decisions in an entirely different manner, and their 'fellow countrymen' can't really be held to account for the behavior (or lack thereof) of their 'representatives' ... we very often wish we had the ability to recall them all, especially those we never got the opportunity to actually VOTE for, but who seem to hold the VAST majority of the actual POWER, but these are matters that can only be handled 'in the long run'. Again, apologies ... and very best wishes in the struggles.
Air strikes are the least 'intrusive' as far as showing a continuing presence in a particular area. Additionally, if the ground forces are local, then them winning the war can ensure the continued primacy of the new ruling faction. When the Western nations get involved, we have to plan a return to 'normalcy' for the nation. However, we are still left with a power vacuum when the western military departs. Witness what has happened in both Iraq and Afghanistan: we have actually made known plans to leave before and insurgent groups bullied the local forces, causing the nation to back pedal.
This is purely from a military perspective, not taking into account any number of political machinations that might be at work.
It also provides a sense of legitimacy to the operations otherwise the West is accused of Imperialism. They still get hit with this anyway, but to a much lesser extent if boots aren't on the ground.