I'll choose the small, simple, reliable tool over the larger framework every time, if I can get away with having the smaller feature set. I'd go out of my way to make the simpler tool work if I could, to keep the overall cognitive load and complexity of the project down.

I never considered writing my own, I just want a tool to plug in and work so I can focus on the application. I also never thought performance of this part of the stack would be a bottleneck for my use cases.

In contrast, I am happy to use Django over Flask because you can't get away from needing lots of web framework features for a nontrivial web app. The bigger framework is usually justified, especially if it's high quality like Django. But spawning tasks (for my use cases) is just an aspect of the project that can have a simple interface and it doesn't justify adopting a big framework. Time I've invested in Django (going back to 2009) is still paying off for me today, but there'd be much lower ROI on the time I'd have to put into Celery. Unless my projects really needed its complexity, but I think far fewer projects actually require that in practice than their architects tend to think.