I don't want to be snarky, but I do seriously wonder how many people really cared about calculus when Newton/Leibniz developed it. It honest couldn't have been more than a handful because Newton slept on it for the better part twenty years.
I honestly think Math as a field has always been defined by "problems that only a handful of people care about".
The only exception I can think about is maybe basic addition and multiplication.
Yes, exactly. A whole lot of math problems were not interesting until we got relatively fast digital computers as they would have taken till the end of the universe if done by hand. Then suddenly it becomes a product you can implement in a library and perform simulations of reality on. Now suddenly a lot more people are interested in the math because improving the algorithm could lead to millions in power saving, or it could lead to far higher accuracy.
Simply put, it's very hard to predict the usefulness of math at the time it's created.
I honestly think Math as a field has always been defined by "problems that only a handful of people care about".
The only exception I can think about is maybe basic addition and multiplication.