I write as little of my own code as possible. Other people's code is better than mine; it's more throughly tested, it's faster, and it's smaller. I use Bootstrap because I know it works on every browser, every iPhone, 20 flavours of Android, Windows Phones and Playstations. If I wrote my own code I'd have to charge a client for 6 months of my time just to get to where Bootstrap is now. Same goes for React or Angular. Writing your own code is fun, but if you want to do things properly you don't have time.