Simple UI - the most popular components used in many web applications

I like the minimalist design / setup, but why use yours and not bootstrap and a similar minimalist style(sheet)?

Bootstrap is good if your client doesn't care about design and want to have his project as quick as possible. In long term development where the client wants to have custom design and custom controls you should use something different. Bootstrap is awesome for MVP but if your product wants to compete with other solutions you can use my code and modify appearance as you want.