Good question and unfortunately there is not a single reason. So many things seem to have a possible contributing factor towards artery disease and it's still unclear which combinations generate the greater risks. You have mentioned some important factors, but there are still a few more.
Research on chimps across various zoos have shown interesting results. Where chimps seem very happy with their environment, whereby they can run their normal social behaviours, they don't seem to contract artery disease even at a late age. In zoos which the environment was not suitable, artery disease was present even in middle age chimps. Chimps in the wild are difficult to test accurately because their natural habitats are under threat anyway, but in sanctuaries where rehabilitation is taking place, their health seems pretty good.
Thanks to the human genome project, comparing genes across different groups of humans has become so much easier. Groups of people with artery disease and groups without were cross referenced and a handful of genes were seen to be different. However, it will take a lot of research now to understand these genes and their impact on the repair ability of arteries.
We have all seen the pressure put on people regarding the consumption of fat. It's almost every day you hear someone look at fat and say "ooh instant heart attack". However, even in many people who carefully control their fat intake and eat 'healthily' there seems to be an increase in disease. General consensus among experts now seems to be that fat is not the big cause which we believed. It is obviously a contributing factor. New focus seems to be aiming towards processed sugars which cause an increase in triglyceride levels. The discovery of a second type of LDL lipid and one which caused heart disease if high enough in volume has caused great excitement. Normal LDL is actually quite healthy, which isn't surprising as all of the body requires it, even the Brain. Why would the body use a product which kills us. It is becoming more apparent that when we consume lots of processed sugars in our diet, soda drinks etc, then our Livers mass produce the nasty very dense LDL which destroys our arteries. This explains a lot, while people reduce fats, they seem to be on the same level or increased sugar intake. Healthy instant package meals, usually carbs, found in stores are packed with sugars to make them taste yummy. Natural sugars, found in fruit, are absolutely fine, the chemical molecular structure can be properly broken down. If you look at cane sugar in a field and decide to eat some, look how difficult it is. The layers of tough fibre covering the plant makes it very difficult to get to. Nature is telling us something, don't have too much. Fruit is much easier to get into, and this sugar is great.
Battle with food companies.
With society today, it's becoming rarer to find families with the time on their hands to shop, prepare and cook fresh ingredients. This would require shopping virtually every day. Instead we buy packaged foods which last longer. Chemicals used to give them a long shelf life have been found to affect our health. Food companies always win the argument by saying "do you want your food to last hours or several days". We seem to accept the longevity of the food but kill ourselves in the process.
I think governments are fully aware of most of the causes of heart disease, yet to remove the causes would mean a huge change in our society, probably too much for us to handle. We would require far more farming areas because food would be rotting much quicker and do we have the resources. By the time the food reached the shops it would have to be purchased and consumed immediately. Imported foods would likely be rotten by the time we see them. The only hope is to find combating drugs which reverse the effects of the chemicals we consume. We are definitely on a road to self destruction and very little can be done about it unless the planets population seriously declined.
Magnesium deficiency calcified my mitral heart valve and who knows what else. I'm 38 and it was diagnosed last year with the calcification. I've had a magnesium deficiency for a very long time but had a severe deficiency for 2 years.
"If calcium is not taken with magnesium or it if it is not highly absorbable, it will cause much more harm than good. Unabsorbed calcium can lodge anywhere in our body. For instances, if it lodges in your bones and joints, it mimics arthritis; if it lodges in you heart, it mimics arterial lesions. Calcification or calcium poisoning can manifest as heart disease, cancer, wrinkled skin, kidney stones, osteoporosis, dental problems, bone spurs, cataracts and many other health problems. Calcium deposits in the joints are called arthritis; in the blood vessels it is hardening of the arteries; in the heart it is heart disease, and in the brain it is senility." - excerpt from "Calcification and Its Treatment with Magnesium and Sodium Thiosulfate" by Magnesium for Life