By the 1940s and 50s, computers were already being used for practical and useful work, and calculating machines had a _long_ history of being useful, and it didn't take that long between the _idea_ of a calculating machine and having something that people paid for and used because it had practical value.

They've been plugging along at quantum computers for decades now and have not produced a single useful machine (although a lot of the math and science behind it has been useful for theoretical physics).