Because exponential growth is unsustainable
Not inherently. It depends on the rate of growth and what is growing. For example, a 1% per year addition to bandwidth is exceedingly conservative, based on historical evidence.
it is bound to cap at some point in the near future.
physical parameters have physical limits, which are constants.
So unbounded growth is unsustainable. Even linear growth.
However, with less than exponential growth one can expect it to be negligible
from some point on (that is, less than x% per year for any x).
Looking at the past data and just extrapolating the exponent one sees is a myopic
reasoning: the exponential growth is only due to the novelty of the given technology.
It will stop when the saturation is reached, that is, when the physical limit of the parameter
in question is close.
If you want a concrete example, look at the CPU clock growth over the next few decades.
Define 'near future'. Is that 5 years, 10 years, 40? And what makes you say that? It's easy to make a general unsupported statement. Don't be intellectually lazy. Show the basis for your reasoning, please.
I'm not making predictions on constants that we don't know; but when speaking
about exponential growth it is not even necessary. Want to know how fast the exponent
growth? Take your 50% growth, and just out of curiosity see for which n your (1.5)^n exceeds
the number of atoms in the universe. Gives some idea. Yes, you can put 1% or (1.01)^n, the difference is
not important.
Of course one can say, let's put it 50% per year until the bandwidth stops growing that fast,
and then we fork again. But this only postpones the problem. Trying to predict now exactly when this happens, and to program for it now, seems futile.