What is wrong with a file for this? Sounds more like a local log or debug output that a single thread in a single process would be creating. A file is fine for high volume append only data like this. The only big issue is the format of that data.
What benefit would a database bring here?
That is essentially log data or essentially equivalent. Log data does not have to be human readable, it is just a series of events that happen over time. Most log data, even what you would think of as traditional messages from a program, is not parsed by humans manually but analyzed by code later on. It is really not that hard to slow to process log data line by line. I have done this with TB of data before which does require a lot more effort to do. A simple file like this would take seconds to process at most, even if you were not very efficient about it. I also never said it needed to be stored as text, just a simple file is enough - no need for a full database. That file could be binary if you really need it to be but text serialization would also be good enough. Most of the web world is processed via text serialization.
The biggest problem with yaml like in OP is the need to decode the whole file at once since it is a single list. Line by line processing would be a lot easier to work with. But even then if it is only a few 100 MBs loading it all in memory once and analyzing it all in memory would not take long at all - it just does not scale very well.