Eventually (in the very near future 
) Monzo will shift towards sending debit cards via the post! 
It’s currently being tested 
but in the mean time while the numbers are low / the current accounts are just getting started, Monzo want to keep a good level of control on sign ups, etc. 
A few people have started receiving magical letters through their doors!
https://community.monzo.com/t/so-this-just-dropped-through-my-door/15449