From Peter Drucker's Innovation and Entrepreneurship (emphasis added by me) —
“The Russian economist Nikolai Kondratieff was executed on Stalin’s orders in the mid-1930s because his econometric model predicted, accurately as it turned out, that collectivization of Russian agriculture would lead to a sharp decline in farm production. The “fifty-year Kondratieff cycle” was based on the inherent dynamics of technology. Every fifty years, so Kondratieff asserted, a long technological wave crests. For the last twenty years of this cycle, the growth industries of the last technological advance seem to be doing exceptionally well. But what look like record profits are actually repayments of capital which is no longer needed in industries that have ceased to grow. This situation never lasts longer than twenty years, then there is a sudden crisis, usually signaled by some sort of panic. There follow twenty years of stagnation, during which the new, emerging technologies cannot generate enough jobs to make the economy itself grow again — and no one, least of all government, can much about this.
“The industries that fueled the long economic expansion after World War II — automobiles, steel, rubber, electric apparatus, consumer electronics, telephone, but also petroleum — perfectly fit with the Kondratieff cycle. Technologically, all of them go back to the fourth quarter of the nineteenth century or, at the very latest, to before World War I. In none of them has a significant breakthrough been made since the 1920s, whether in technology or business concepts. When the economic activity began after World War II, they were all thoroughly mature industries. They could expand and create jobs with relatively little new capital investment, which explains why they could pay skyrocketing wages and workers’ benefits and simultaneously show record profits.”
Of course, the Kondratieff industry cycles don't apply to every industry and are hardly proven.
The key takeaway is that industries which no longer need additional capital to scale can see increasing profits simultaneously with increasing variable costs, but the increasing profits are a short-term phenomenon.