There is a known negativity bias in human thought; events and narratives which produce more negative emotions acts as stronger attentional attractors than positive ones, and because of this are stored more comprehensively in memory. See this page for more details. Hence these things stand out to us to a greater degree than an objective appraisal of the situation would warrant.
Another factor, not related to psychology but to the way the universe functions, is that entropy (roughly,chaos) is simply more statistically likely than negative entropy (roughly, order), which over time causes closed systems to become more chaotic. Imagine a deck of cards organised so that each suit is ordered from ace to king. Any random shuffling of that deck is much more likely to produce a less intense pattern than that which unifies the deck in the ordered instance (ace to king across all suits), and the fragments of linear patterning of adjacent numbers/symbols will become less orderly with increasing shuffles.
Since lifeforms such as ourselves are fundamentally based on the processing of negentropic forces (to take a basic example, food is more orderly than excrement), and since excessive entropic forces are damaging to our structural integrity, we have developed value systems which generally prefer negentropic forces, that is, processes with high levels of order, as opposed to more chaotic processes. So, entropic configurations we generally deem bad, and negentropic or orderly ones we generally deem good (this is a very general principle, which doesn't hold in all cases, but the gist is accurate). But as I described above, there are statistically many more ways for things to be disorderly than orderly, therefore we are more likely to encounter situations which have a negative outcome than a positive one, simply because the range of our expectations for what is 'good' is a small and delicate bubble which lies within an infinitely larger space of 'bad' possible outcomes.
One last thing... you mentioned that it is 'bad' things which are generally reported on. This is simply the economic exploitation of the general negativity bias of human minds. Since our attention is more fixated by negative narratives than positive ones, that is what is generally reported on. It is also that the magnitude of entropic disruption to human systems is generally much larger than the negentropic elevation of order within those same systems, since they are generally organised to operate as near to minimum entropy as possible at any given time (at least idealistically), kind of like homoeostasis on a societal level. Which is not to say that positive discoveries are never made, in fact they are made frequently... it is just that they are rarely if ever reported on in the mainstream media.
You said that "The LACK OF proper nutrition is terrible, while very good nutrition make no marked differences. The LACK of moderate exercice is horrible, an optimal setting do nothing more." Logically, this is incoherent; you're saying that '-A = -X but A = 0', when the proper inversion of that is 'A = X' ie good nutrition makes an excellent difference.