You said "that Django still lacks". Django no longer lacks CSP and background tasks.
Regarding my edit, you need to differentiate between different types of jobs. Sending an email is okay to do in process. Other (mostly async) Python web frameworks have implemented this, so the Django team probably felt compelled to offer the same.
Processing a user-uploaded file is much more expensive and shouldn't be done in the web process. If enough users upload files you're starving your workers for CPU.
Regarding my edit, you need to differentiate between different types of jobs. Sending an email is okay to do in process. Other (mostly async) Python web frameworks have implemented this, so the Django team probably felt compelled to offer the same. Processing a user-uploaded file is much more expensive and shouldn't be done in the web process. If enough users upload files you're starving your workers for CPU.