The size is less relevant - you only use what you need.
The other main reason I chose Django for a particular project is the ease at which I can find experienced developers afterwards. Not that it really matters that much, Python being Python, but its easier to find someone with Django experience than one with Flask.
Not really. Because its python, its all Python devs. But if you want someone with specific Django experience, you'll find it easier to find than flask. Popularity wins and Django is popular (for a good reason)