You're getting some things mixed up.
We must be careful when comparing tangible goods (like food) to intangible goods (like a browser app).
Food has an element of genuine scarcity. This scarcity is what causes food to have economic character. If there is more demand than supply, this state of things triggers investment into the production of more food to satisfy the demand some time in the future, ultimately affecting prices. Prices will rise in the short-run, but decrease in the long-run (if the demand can be met, and then some). If food was not scarce, it would not be an economic good, and it would not be subject to supply and demand.
Software, on the other hand, is intangible. It can be duplicated and distributed, essentially for free, and more or less forever. Even if you have a paid plan this does not create scarcity. We shouldn't think of software the same as we think of food in terms of economics.
What is the theoretical limit to how many paying customers would be so many, that it impacts the ability of new customers to install, pay for, and use your app? Practically, this question is insignificant, that's one of the reasons software is interesting.
The simplest answer to why 40 - 50 people discover your software per day, is that whatever marketing channels you have utilized (or not) up to this point in your apps's lifetime expose you to 40 - 50 users per day who have a direct need that they think your product may solve.
The second element to this is that there are a lot of people in the world. As others have pointed out, they don't all have the same information. You are capturing a fraction of the total number of people out there looking for a solution to this specific problem, who are influenced by, or aware of, at least one of the marketing channels that influence your app.
If the problem your app solves became a non-issue overnight (for everyone), then you would see that number start to decline over time or go away instantly.
What's more likely to change the situation (temporarily or permanently) is that something changes (positive or negative) with those marketing channels, either influenced by you, or by whatever entities or forces control those channels.
Hope this helps.