That's because almost as soon as a new TLD becomes available spammers start using it as the from address in emails. For probably 99.999% of people the only email they will ever see with such a from address is spam. Just automatically marking all mail from those domains as spam turns out to have such a ridiculously small false positive rate and eliminates so much spam that it is worth it for many people.
That does mean that in practice it is probably best to consider most new TLDs as web-only. Use them in URLs but have @com, @net, or @org email addresses for anything where you want outgoing mail to get through.
When I was running my own mail system, I eventually ended up with all of the following TLDs going straight to a spam folder:
accountant bid christmas click club cricket date download faith gdn gq help info link loan men party press pro racing review science site space stream team top trade uno webcam website win work xyz zone