there are indeed several reasons, but in this case I suspect the problem isn't even with the matplotlib (well, most of it). You mention traces that are GB's in size and that's the first big problem.
For reference, the newest Zelda game is a total of 18.2GB of storage, and of course Zelda isn't trying to audit the entire game on every load. Games spend a lot of time making sure their assets are lean, and at the end it is deployed in some binary format to further reduce its impact on a game. trace files that focus on human readability lose this compressibility.
So regardless of how fast the graphical plotting capabilities are, I imagine such an app is CPU bound from simply trying to parse that trace data. That'd be the first place I'd look to optimize (you know, without properly profiling your app. Probably something I'd say in an interview setting).
For reference, the newest Zelda game is a total of 18.2GB of storage, and of course Zelda isn't trying to audit the entire game on every load. Games spend a lot of time making sure their assets are lean, and at the end it is deployed in some binary format to further reduce its impact on a game. trace files that focus on human readability lose this compressibility.
So regardless of how fast the graphical plotting capabilities are, I imagine such an app is CPU bound from simply trying to parse that trace data. That'd be the first place I'd look to optimize (you know, without properly profiling your app. Probably something I'd say in an interview setting).