A falling rate of profit is accentuated to the extent that moral depreciation shortens the time during which fixed capital functions and reduces the total mass of value and surplus value which it forms, making the valorisation of the given capital worse and cutting short the period of accumulation.
However, that would mean the profit rate is maintained at the expense of stagnation, viz. massive idle capital and idle people since dept I would not be churning out new machines as capitalists sit on a mountain of physically durable capital they are unwilling to scrap to bring on new low cost capacity.
If demand falls to the point where the level of production could only be maintained in material terms by cutting short the life of high cost assets and introducing new low cost capacity, sufficiently monopolized industries may choose instead to restrict production to maintain prices while amortizing that high cost capacity. The long life of assets would be a noose on society's power of renewal.
'And if capital formation were to fall exclusively into the hands of a few existing big capitals, for whom the mass of profit outweighs the rate, the animating fire of production would be totally extinguished. It would die out." Capital 3, p.368
yours, rakesh