Because there was no way to make money on it. Before the Age of Discovery, there wasn't much money in being able to find out one's coordinates in the open sea - and Age of Discovery only started because a long, grinding war to liberate Spain and Portugal from Muslims had to finish first to provide both economic base for seafaring, and safety of sailing too. And maths mainly developed for the goal of improving navigation.
Newton was Master of the Royal Mint for something like 30 years and put people to death for clipping coins. He spent decades trying to manufacture gold. I would say money was a very big motivator. Don’t know about Leibniz.
That wasn't his money, though. He apparently received a salary between £500 and £600 per year, While that was a lot more money than it is now, an inflation calculator at the Bank of England suggests that it was the equivalent of around £43,000 today (around $US53,000 at today's exchange rate).
Not starvation wages, certainly, but neither was it vast riches.
IIRC the money motivation for Newton made him pursue alchemy, that didn't lead anywhere and just wasted time that would be more fruitful if applied to calculus and physics.
> made him pursue alchemy, that didn't lead anywhere and just wasted time that would be more fruitful
You wouldn't have known in Newton's time if alchemical transmutation into gold worked. Certainly, you knew then that some substances could be transformed into other substances, and it was such research that developed into modern high-school chemistry.
