There's a clear philosophical difference between a framework like NextJS and Rails/Django/Laravel. The former takes the approach of expecting users to integrate various third party libraries (ie. Prisma, PassportJS, ReactAdmin, etc) while the latter has it a lot of features built in as framework primitives and defaults.
Some of those features:
* ORM and DB migrations
* Auth
* Admin interface
* Form handling and validation
* Email sending
* Background jobs
Which is why you end up needing so many different SaaS templates for Nextjs that tie all these different libraries together into a pre-built package.