You (well, maybe not you, but one) can also imagine all kinds of counter-arguments (not that I know if any of these are true or not):

- Devs would rather spend their time on development

- No one is inspired to move the system over

- They have automations or conventions built on Trac

- Their super users (prolific users, testers, and engineers) are all used to Trac

- People use RSS feeds (Trac has lots of RSS feeds) to stay informed or build other tools, which would all have to be migrated and might have incompatible formats

I encourage you to be more open-minded about the way others choose to work. We shouldn't overemphasize homogeneity in work processes. I also encourage you to be more generous with the words you choose.

For a mature project such as FFmpeg, migrating to a new bug tracking system may produce some value to a small set of people who are reporting bugs, but for the vast majority of FFmpeg users, it produces no value.

So in this particular case it seems like they are willing to sacrifice the convenience of a small subset of users in the interest of the whole user community.

This applies to many mature and long running projects.