and what can we do about it?

Overly densed Population (more people in small area)/condition of road/condition of vehicle.

Every one knows the reasons, from a child to the city planners.  You raised a good thread but you left others to answer it. We would love to read your input too.
1) Too much construction work and poor way to transport construction materials.
2) You can dump anything on the road which is free of cost, you can squeeze the road and it has been done by mahapalika too.
3) No long term plan because there is no personal benefits, corruption and ugly politics, undue interference by political party just to politicized the issues but not for corrective action works the best.
4) This is very true proverb "जो अगुवा उही बाटो हगुवा ',
5) The rich are morally not leading as example  but we point out to the poor people and always look them down, majority are poor.
6) Can we arrange bins for garbage collection will serve but  I do not think so, that bin may be taken away by the evening , we need those stuff and enough room as free gift.
7) Every time I attend  party my mind and head looks around and most of us even living in new culture for a long time,  we have having hard time to adopt new things, I mean we still leave our plates on the table where person next to your seat is putting away his dirty dishes and  where  the garbage bin  is awaiting for you in the corner.
8) I mean do we care about these things? No, personal convenience always comes first not what is right or wrong.
9) Not trying to be sarcastic but the truth is, some of our communities love to throw things on the road, even that reaches to their own bed room. What do you expect from them?
10) We do not think collectively rather individually where things need to be collective way.
There are tons of things we can write but the bottom line,  it solely depend on our thought process. Most of us  like to have maids, if not we like our mother and sisters to serve us  and enjoy the life and it reflects every aspects of our lives. If you eat banana then you will be throwing to the footpath so you can laugh at the victim of your cruel intention.

asteroids dude. they fall on ktm more than anywhere else.

i think they have to bring those trucks from US whih will soak all the dusts from the ground, rather than wasting money on corruption why don't they spend money on those technologies

Technology will fail on Nepalis' mentality. Udyapur cement factory and many others had been closed not due to real break down but in induced by management.

Reason for dust:

1. Road condition: All roads should have black asphalt coating to prevent dust from forming.

2. Construction practices: You can pretty much do what you wish while constructing, hence allowing dust to fly free.

3. Vegetation: There is a lot of empty lots without grass. Such can easilty dry up forming dust.

4. Cleaning: Not enough.

Neta ra janata jpt gardai basne... YoTaBhayanaNiSom.

www.reddit.com/r/nepali

The real cause is all filthy politicians and filthy politics in Nepal.

do you guys think that Kathmandu being a valley has some part to play in it? Most of the trapped dust never gets out of the valley due to the hills. Are there any major cities in the world with similar problem?

When I was in college and bikram tempus were all over the cities, one of
our friend suggested we need to put coupe big jumbo air fans to let the
filthy air out of the city. May be with solar and wind mill we can
think about that.

It is not possible when government is 1000% corrupt and peoples are okay with every situation.

We must have civic sense and I have no clue how to improve it.