Yes, resetting the tibble is probably inefficient, but for now building the tibble one column at a time is easier to do. That may or may not be an practical issue depending on the amount of data that will be put into the tibble. If it is a practical issue there are a number of ways to fix it. The app is not building tibble literally, it is building it dynamically, i.e. deriving the data, including the column names, from a number of input files, which almost always leads to time/space/complexity tradeoffs
You don't actually need a named list here to make a tibble but it is almost always the best thing to do and in some cases necessary... but I left that out to simplify the example and it wasn't part of the issue I was looking at.
In the actual code the column names are passed in as a variables which complicates things. There are a number of ways to handle that issue but again it would complicate the example.
In the end the app will build a list of tibbles from an arbitrary list of files (which can have different formats), with each file contributing some data to each tibble. It's not a simple "rectangular file" so the simple ways of building a tibble won't work.
Dan