You've omitted the immediately preceding qualifier: "if something can’t be resolved quickly on email, suggest a meeting or simply walk to your colleague’s desk to confirm a plan."

The party sending the email has already 1. signalled importance and 2. your own filter has indicated your agre,ent.

If 1. was in fact false, there's the (perhaps remote) possibility that the sender(s) will come to realise that "send email" corresponds to "I will be interrupted in return".

As an organisational norm, this is likely a Good Thing to cultivate.

Letsop's principle: be conservative in what you accept and liberal in what you send.

You're inferring that the only option is to interrupt someone, when it's perfectly possible to schedule a meeting or send a message asking them when they can make some time for a quick chat.

Schedule is predictable well in advance. Interruptions aren't.