Much of the bloated and inefficient code out there is the result of simply pulling something off the shelf and using it, just because it 'kind of' does what you need.

Nevermind that a much simpler and efficient piece is possible, we have to ship ASAP so don't bother to spend any time on it.

Include a whole set of dependencies just because we need a function or two in a huge library or framework. Worry about optimizations later (i.e. never).