Sometimes you just want for code to be able to run at all, even with a sizable download, if it means you don't need to do any porting work. For example if you have many years of work on a codebase, and you can run it on the web with almost no effort, that can be really useful.

I agree that we want most things on the web to be optimized for the web. But sometimes business or other reasons matter more than code size.