If you use it as just a CSS include then I agree with you in a sense. But typically or rather optimally you use it with Sass/SCSS and override Bootstraps varia

If you use it as just a CSS include then I agree with you in a sense. But typically or rather optimally you use it with Sass/SCSS and override Bootstraps variables so Bootstrap generates its classes based on your input. Related: One of the goals of Bootstrap 5 is for example a stronger shift towards utility (atomic) classes. In 4 you can already generate their utility classes based on your variable declarations. In 5 this will get more powerful and the API becomes cleaner. Another goal is to improve documentation for users who integrate with Bootstrap SCSS this way.