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The reasons for code bloat are typically not visible to the user. Cross platform libraries, OO programming, etc...
The scaffolding that is holding these large projects together is what is causing the bloat. You need the scaffolding because it is the work of disparate teams. There are better ways to do it, sure. But it is the develpment process and the code scaffolding required to make it work that is bloating our code.
This is even more the case in OSS because the people doing the programming are from all over the world, with different skill sets.