We call it a three-day funeral, but the process can sometimes take as little as 36 hours (death in the evening of first day, burial/cremation in the morning of third day). I think the short funeral also helps the bereaved return to normalcy sooner. There's no time to get used to the funerary mood. You're expected back at work/school/etc. by the fourth day.
1. They are removing all of this guys body fluids and injecting him with weird preservatives. He's been drained like a hunted animal and is puffed up with fake juices.
2. This person died and they are extending the time between death and burial for the convenience of those attending the funeral, because the death of a human being is somehow a thing we should "work into our schedule" and not expect to be TOO inconvenienced by. Like seriously? What better way to honor this guy than to be like "yeah, I know you died, but can you just hold on a sec because I really need to let my work know I won't be there for that meeting." It's so detached from the reality of what has happened.
For ordinary people, though, the immediate family is all who matters. To continue to Korean example I mentioned above, it is culturally accepted that you can just drop everything and leave if a family member has died. You don't work the funeral into your schedule; the funeral forces itself into your schedule whether you think you can afford to or not. I think this is a result both of the Confucian tradition (filial duty above everything else) and of the practical necessities of public health (you don't want to keep dead bodies around for too long in a hot and humid country). The flip side of being able to drop everything immediately, of course, is that you're expected back at work as soon as it's over. Either way, social norms need to support this kind of prioritizing in order for most people to adopt quick funerals.
And land shortage is not really an issue in any real sense. Even in a place like China or India you could find enough land to support natural burial practices like I described above. If you begin with the assumption that most people want to be buried, there are plenty of options that can maximize the use of existing land. You can bury more than one person in a single plot over time (as one decomposes, put another in) or you can go deeper and do things like bury people in tunnels. If people want a solution, they can come up with one pretty easily, it's just a matter of actually trying.
My plan for years now has been to get buried in a wicker coffin in a forest. Not an enclosed coffin, no embalming, no neat graveyard, just as natural as possible underground with a tree on top.
If you're buried won't you turn into methane and then CO2 anyway?
Still, animals die and decay in the wild, they don't get cremated in the wild[0]. That suggests to me it's the more natural and sustainable way to end.
[0] Except in forest fires, I suppose.
Lots of people think cremation is environmentally friendly, but they don't realize the amount of fuel being burned and how much carbon it puts into the atmosphere. It's not clean by any stretch of the imagination. They also don't realize that crematoriums are not cleaned well and that they are often not getting the ashes of just their relative but probably other people as well, but that is a separate issue.
The answer is for funeral homes to begin offering expedited burials that use natural preservation techniques on unembalmed bodies. The new expectation would be that the burial occur within 24 hours of death, 48 if absolutely necessary (something that would be inconvenient for funeral preparations, but worth it) and bodies placed in freezers and on dry ice (in the coffin) to prevent decay and odor from setting in.
This works, it's being done in certain parts of the US and in lots of places around the world. My family is Eastern Orthodox Christian and this is the traditional burial method for us. A simple wooden box, an unembalmed body, and into the ground ASAP. Nothing better for the environment than to return yourself to the earth.