Why exactly does a lower rate of profit cause a crisis in capitalism?

So, I understand the underlying logic behind the TRPF

In short, capitalist tries to expand relative surplus value (has to in order to remain competitive) -> greater organic capital composition over time. ROP = s/(c+v) = (s/v)/(c/v+1) if c/v grows faster than s/v then the overall economy wide rate of profit falls, and marx argues this will happen as a result of growing capital investment (i.e. c/v rising fast over time). Granted, this is a tendency, particular technological innovations may expand s/v faster than c/v in the short term, there may be an increase in absolute surplus value, etc. But point is, in the long run if c/v grows faster than s/v the whole ROP falls.

Here's what I don't fully understand: why exactly is a lower rate of profit a catastrophe for capitalism and why is it the center of "crisis theory"?

This lower ROP is felt by everyone in the market, not just a few firms, so there is not competitive advantage/disadvantage here. I can see the argument that it reduces the total mass of investment available, as there is less reason to invest (what do capitalists do with money instead? speculation?)

But like, I get that the very core of capitalism is accumulation, and a lower rate of profit means a lower rate of accumulation which is like not great for the capitalists. But I don't fully get why it leads to systemic collapse or crisis. Slow growth can mean a recession I suppose.

I also get that this means that there is basically a huge mass of capital that cannot really be profitably invested, meaning that overall investment falls.

I guess I don't fully get why systemically capitalism has to constantly grow. I get this on an inter-firm level (competition means you have to in order to survive), but on the entire system level there isn't competition.

Basically, the argument for this leading to a problem or firm collapse that I can see is that the higher organic composition of capital means that, per unit production, fewer workers are needed. Workers are the primary consumer base of industrial production (even if you primarily sell to other capitalists, their base is workers, and if their base can't buy, they can't buy). So by investing in capital, you reduce the overall mass of consumer demand. This can be offset if overall economic growth and profitability is greater than the loss in demand for workers (so like, sure, on a per unit production level I need less workers than I did before, but I'm producing so much more that the absolute mass of demand for workers still rises, or there a new firms or new profitable industries with demand for workers that offset my loss in demand). A lower rate of profit -> less investment & growth -> no more offsetting the effects of capital accumulation. One real way to solve this is more profitable investment outlets to thereby stimulate demand for workers. But, if we think like this, then the problem here is a lack of demand. Now that lack of demand extends from massive overaccumulation. So like, even kenyesian demand management strategies are a best a short term salve, because you still have an economy structured that's oversaturated with capital? Is that basically correct? I'm not sure, cause idk if a marxist analysis would focus as much on demand as I did here, and potentially mesh with some kinds of kenyesian solutions (though again, the keynesian solution doesn't solve the fundamental overaccumulation problem)?

Thanks!