Stagnation is death. While gratefulness may be considered a virtue to many; to not ask for more and to accept what you have, it is highly counter-rational given that everything in this universe is only successful because it is inherently greedy. Life is pure greed, and if life sees success despite being grateful or lazy in some way, it is always in spite of that aspect, as it is greedy in other, more subtle ways. Greed is the primary drive and everything falls below / is secondary.
Those who no longer seek to improve, to adapt, to surpass themselves and others, to seek "out of their league", - get shit on in many ways. The food chain, an inherent mechanism to this reality, values apex predators who do not care much for others below and who value themselves more than anything. The universe loves creating bullies : smarter organisms who are not only more in tune with reality, understand it better, but use their understanding to shit on everyone below them. And those who do not take power or desire power ultimately get shat on or wiped out.