A properly secured seed should never come in contact with the internet or be stored digitally. Paul's seed was used on a software wallet, an app that is considered a hot wallet. If his software or computer experiences a breach, gets hacked, or infected with malware, an attacker could get his hands on the private keys like it was mentioned amongst the replies. Whoever has the private keys/seed, owns the money they protect.

Even if such a breach didn't happen, it's better to create new wallets and get a new seed than using the same seed across multiple software. 1 piece of software represents one item that could be attacked. Replicating the same private information across new apps creates 2 or more attack vectors and ways to lose your coins. Compare that with sharing a secret with one person vs sharing the same secret with 3 people. With 3 people knowing what you know, the chances of someone exposing you have increased greatly.