“On the other hand, every particular sphere of capital, and every individual capitalist, have the same interest in the productivity of the social labour employed by the sum total of capital. For two things depend on this productivity: First, the mass of use-values in which the average profit is expressed; and this is doubly important, since this average profit serves as a fund for the accumulation of new capital and as a fund for revenue to be spent for consumption. Second, the value of the total capital invested (constant and variable), which, the amount of surplus-value, or profit, for the whole capitalist class being given, determines the rate of profit, or the profit on a certain quantity of capital. The special productivity of labour in any particular sphere, or in any individual enterprise of this sphere, is of interest only to those capitalists who are directly engaged in it, since it enables that particular sphere, vis-a-vis the total capital, or that individual capitalist, vis-a-vis his sphere, to make an extra profit.” (p 197-8)
It is easier to see why this objective reality is, however, apparent to the capitalist at a phenomenal level. Every capitalist can see that if the level of productivity increases in the economy, they benefit for the reasons Marx describes here. Each can see that higher productivity means lower unit prices for commodities. Lower prices for wage goods means at the least less upward pressure on wages. Each capitalist may not understand that they share in the pool of total surplus value, but they do understand that their own profits are higher if their wage bill is lower.
But, as Marx pointed out earlier, as surplus value assumes the phenomenal form of profit, and as the capital advanced assumes the phenomenal form of cost price, there is no reason why capital should consider a lower price for labour any differently than a lower price for any other input. In fact, for those businesses that employ large amounts of constant capital as opposed to variable capital, and who at a phenomenal level, see their profit rise as their cost price falls, it will appear far more important to obtain a reduction in the price of their constant capital than in their wage bill.
And, of course, a rise in the general level of productivity will bring that about too. As commodity prices fall, as a result of higher productivity, the costs of the materials, machinery etc. they need to buy, falls, and the same processes will reduce other costs of transport and distribution. At a personal level, the capitalist will also find that the price of things they buy for their own personal consumption will fall, thereby enabling them to enjoy an even more lavish lifestyle and to have more of their profit left over for accumulation.