For short living projects, say two moths or half a year, I would probably go with an existing framework, for that initial speed and reuse of existing libraries/plugins. But for anything you would spend one year or more on, I would build a custom solution which optimizes for whatever is the domain priority, for example front-end performance, speed of development, etc. If you use your own "framework" it will become stable over time, where as a popular frameworks like React or Angular will just keep changing and eventually reach end of life support.