Which has an interesting balance: you're then using things developed in isolation, which can give you better parts but it definitely means you have to provide interconnect conventions and that new developers have to get used to your particular combination of parts.

If you think you can do this better than the Django community, this can work out well but I'd say more often than not when I've heard about it people weren't actually able to spend enough time on this as they'd hoped and keep falling further and further behind Django and other frameworks.