Not using constrained() in the default user migrations

[Muffinman]

Is there a reason for not using constrained() in the default user migrations?

e.g. in the recently added sessions table (laravel/laravel@feded74), the user_id column is not constrained to the users table immediately above it.

I'm wondering if this decision was deliberate and if so what was the reasoning?

I've always used constrained() myself to ensure DB consistency and make sure old related data is cleaned with cascadeOnDelete() etc. I just wanted to know if there are some unforeseen issues with using constrained() that I am not appreciating?

Thanks!