Christian systems, say, make what is right into what is in your rational self-interest through the causal structure of morality (see here). By coinciding these, they gain a potentially relatively robust motivational element. For example, stealing something might be ostensibly in your rational self-interest. The Christian system postulates that God will punish you for doing so, and reward you for not doing so. Therefore, it is actually in your rational self-interest not to steal (assuming that there is a God, and so on).
Contemporary secular academic philosophers’ moral systems have lost this dynamic. Because they are atheistic and so don’t include a Heaven, Hell, or Purgatory (say), any appeal to rational self-interest must be done ‘this world’. Often, however, self-interest and the morally right thing are in conflict in this world. Realizing this, secular academic philosophers simply jettison rational self-interest as having to do with morality (for example, see here).
Instead, doing what isn’t in your rational self-interest is celebrated, and in particular they conflate what is ‘right’ at a societal level with what is right at a personal or moral properly speaking level – hence gaining the appearance of having a personal motivation for overcoming self-interest, when they have really just introduced semantic confusion (for example, see here, or consider Rawls’ ‘veil of ignorance’ as a purported guide to determining the moral assessment of a situation, perhaps). Yet, because it is not plausible that not appealing to self-interest in some way (whether directly or indirectly) can sufficiently motivate people to moral action where what is right conflicts with apparent self-interest, their moral systems become, in a word, ‘academic’ and, indeed, parasitic on existing moral systems that do have relatively robust motivational elements.
To come up with a workable moral system, one must curb ostensible self-interested behaviour that incurs a societal cost by showing how rational self-interest coincides with various societal goods. To not have a motivational component leads, effectively, to moral nihilism.