>>37798
1) To read individual pixels from an image. With local files, I can load any file from the filesystem (not limited to game directory, so I could even load something like C:\Users\You\VeryPrivateFile.png). I can display and draw them to other canvases, but I can't get a single byte of image data without error. Even canvases on which these images were drawn get 'tainted' as per chrome's terminology and they behave the same. The goal of this mechanic is most likely to prevent scraping your private data and sending it to random remote servers.
Granony's other game, Ryona no Kane reads pixels directly, so if you download it, you will run into errors when attempting to run locally. For TC, stuff like >>37348 was impossible to implement using local files.

2) The updated physics engine won't load without it. Box2D is pretty old and the 2.x.x used a version from 2013 transpiled from ActionScript (Adobe Flash's language). Needless to say that version was not maintained, so no leaks and bugs were mitigated, and no additional features were added. The currently used version of this lib is compiled to WebAssembly, something which did not exist back then, is more stable, and way much faster, and I think these outweigh the the lack of file:// support.