@prahladyeri I think the migration to Symfony, developers had to learn the Drupal framework again.
At least this got me scared of 😅
Also take a look at https://backdropcms.org/ which was a fork of Drupal 7 before migrating to Symfony.
Server run by the main developers of the project 
It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!