The first version of the application that is using these tables is more than 20 years old. Gradually stuff got added. There is work on a webapp. That started quite some time ago, but 4 years ago in earnest. Unfortunately, it is far easier for one man to add something to that old app, than for a whole SCRUM team to add that same change to a webapp. Feature parity is still some way off. Then again, of course the webapp does things the old one cannot, like a shared database between different locations and seamless integration of other online services. And those two things become increasingly important.
And of course, far more developers have a job building that webapp
The power of FPC/Lazarus is that you can build something that works very fast, especially database applications. The problem is that people who programmed in Delphi get scarce and it is seen as something old and depreciated. It's better to use the development tools and environment everyone knows than lobby for the use of a better one they don't. And it has to run in a browser, of course. Distributing and installing applications automatically never got off the ground.
So, in time the old, file based databases will slowly disappear. But in the mean time, it's much easier to roll out applications if you don't need to install an SQL server at each location. And as webplatforms assume a single connection to the database with admin access, you are required to build a backend as well. Which requires rolling your own (AJAX) communications, etc. It's far more work.