I mean first of all what is "quickly"? Like if you know nothing and learn something that is an incredible pace un-matched by knowing something and adding more.
The other thing is that we might actually be more capable than 18th century folks in general due to a lack of malnutrition and a much better access to information. That being said those who were able to do science in the 18th century were likely well off and quite capable so not sure there's that much of a difference after all (evolution probably happens on longer time scales).
So I'd guess a major contributing factor is that this growth is to some extend self-propelling. So better nutrition, more spare time and information, leads to better tools, better nutrition, more spare time and more chances to research. So it's not that it's unknown factors. And more people being in a position of being well off and educated leads to more people being able to pursue their curiosities which further increases the knowledge and the tools to improve society and it's knowledge. So some sort of progress is just a matter of statistics, the question is just in what direction.
Now is that non-stop? Well up to a certain point the capabilities of a society increase with the number of it's members, but likewise the management overhead and the space requirements become more relevant. Also the amount of information changes from "too little", idk picture a medieval farmer and "too much" idk picture someone trying to read the entire Wikipedia. So knowledge is not just added it also gets lost so you either need to find compression algorithms that bring the complexity down so that all people can have knowledge and still have capacity left to add more or you might find yourself in a position where you just curate and conserve rather than add to it. Or knowledge might simply stagnate or even get lost because records are destroyed and experts die. Though our improved living conditions also made recording of history faster and easier (think of a portrait vs a selfie).