I think it's more correct to say that the Marxist (well, labour theory of value) perspective is not that the employer is incentivized as such, but they _have_ to. That the capitalist market _requires_ it or it doesn't work, business won't survive. It's intrinsic to the profit / wage-labour model, even if you switch to something like cooperatives or state ownership.

The theory is that surplus value (which can become profit, or be reinvested, etc) exists only through paying the worker less (on aggregate) than the aggregate amount that the worker provides through their labour.

The mainstream economics answer to this is to say that the labour theory of value is bunk and that prices are defined purely by market forces. But this kind of misses the bigger picture of what Marx was getting at rather by getting lost in the weeds about price definitions and really is a critique of Ricardo more than Marx.

Despite using the term "exploitation" which has moral overtones in English, Marx really isn't casting a moral judgement here. It's a technical description. But he does believe that this phenomenon leads to structural inequality and injustice and that the only resolution is some other kind of property ownership or method of production. Though he was famously vague on what that alternative would be, and people far less intelligent than him were left to fill in the blanks with some rather awful alternatives.