I'm not interested in the psychological question of motivations. Talking about the motive as social Darwinism is a way of saying that conservatism turns out to be self-refuting and empty. The systematic effect of conservative policies is the establishing of a regressive way of life that's antithetical to progressive humanism and to the idea that everyone deserves to be treated as people rather than as animals.
Conservatives implicitly prefer monarchies, dictatorships, cults, and the like. The most conservative places in the world are currently in the Middle East, Africa, North Korea, the American rural red states, and so on.
The conservative view of Covid is consistent with this regressive stance. The initial impulse by Boris Johnson was to go directly for herd immunity, to preserve the free market rather than lock it down, and to sacrifice the huge population of elderly and sick people who couldn't fight off the virus. That's what you'd expect from social Darwinians who think of life purely as an evolutionary struggle (and who obscure that repulsive view with religious or otherwise sanctimonious rhetoric to avoid being dismissed as parasites).
The other conservative policy towards Covid was the anti-intellectual American one of denying that the pandemic exists and blaming the problem on scapegoats. That was the cultish, Trumpian line which again was consistent with my analysis: the cults so preferred by these "conservative" Republicans function like animalistic dominance hierarchies; they're run by fear, power, and intimidation rather than by humanistic values of critical thinking, tolerance, and compassion.
I go into more detail on this view of conservatism in the links below: