In any natural disaster,earthquake,for instance,people always rescue human lives first of all.At such times any property seems much less valuable compared to human lives.
My question is :why people not exert to reproduce more lives since they take life so valuabe?
Because a man needs 8 hours of sleep after 3 minutes of ummm, action. Reproduction is hard work for men. 
For women it takes 9 months after the man’s three minutes to pop out one kid. 9 months out of 12 months, at most a woman could pop out 1 kid a year(barring multiple births). Spend your adult life pregnant and you will figure out why women do not reproduce more. 9 months of your body feeling like crap, hormonal mind twisting mood swings, the ability to function normal is gone, and this you want women to go through on an almost continual basis?
Raising just a few rugrats causes what ever sanity and energy you have left over from paying bills to keep the little rugrats in food and shelter to go flying right out the door. Imagine a household of 15 kids or more. Dear God no thank you. I love kids but, dammmmmnnn thats insane!
And you think people don’t value life 
. Birthing and raising just one or two rugrats is hard work. How could you not value your own labor?
well aside from the fact that it is an assumption that we rescue these people because we value human life so much, and a very wrong assumption at that, it should be quite obvious why we do not reproduce more as you call it. More is not always better in nature. Nature is a lovely woman that tells you that it is not the amount that counts, it is how you use it. There are two main strategies in nature when it comes to offspring: 1. quantity: the buckshot approach to life. Create as much offspring as you possibly can knowing that most of them will perish, but due to sheer quantity a few will survive. This approach is seen in organisms that do not raise their young and where the period of youth is as short as possible. 2. quality: raise fewer offspring but take care of them. In this instance the energy and resources are not put in creating ever more offspring but rather in providing for the offspring you have. Protecting them, feeding them, raising them into adulthood so that they have the best possible chances of survival. We humans belong to the latter, like all mammals do. What your values are has little to do with any of this, the more children you need to keep alive the more spread your energy and resources will be, the less effect per offspring it will have, the more likely it is that your offspring won’t survive.
It seems like the capitalist narrative has overtaken this thread.
Bad mojo, that.
Is life’s value directly related to its scarcity in a generalized sense?
Working (making properties or money)also often make life boring and routine,but it seems that people prefer working to make money rather than reproducing,though when disaster takes places,they are much more willing to rescue life than properties.
‘More life makes life less valuable’.seeing by others it maybe true.but as an individual,can one person be disvalued by the amount of his spacies?
Birthing and raising children are hard work for women,so it is women who decide how many lives exist on Earth,and the population of any race.
If no woman willing to take these hard work,is it a hard work of men to persuade them to do the work for the sake of race’s existence : 
.
Life isn’t scarce. The “value” your life has is the survival of the genes first and foremost, the organism second and at a far far distance in some cases the group. Other than that your life has no real value.
And when you complain about the capitalist way of thinking, whatever that may be in this case, it hardly makes sense to then start about value due to scarcity
In modern society,the chances for anyone to confront disaster is the same,the rates or chances of survival are not depending on the energy and resources you spend on your offspring,but largely depends on one’s fortune.There are many disasters happenning everyday:vehicle accident,air crash,terrorist attack,natural disaster,etc,in these cases,the loss of life are much greater a tragedy for one who has less offspring than the one who has more.
I don’t know where you think you are getting this from but not from any empirical evidence, there are huge differences in risks across the board in modern societies. There are also huge differences in available resources for your offspring and as such how much offspring you can provide safety for.
What’s the value of genes if they don’t make up your life?what’s the value of cement and bricks if they don’t make up house?in these cases,the real value of genes or bricks is to make up life and house,other than that your genes and bricks have no real value.