Everything I wanted to say in these two replies.
I think as soon as audiences are allowed, they'll promote on music shows. Since concerts still don't look like a possibility for some time now, I think they'll definitely be on those shows.
I personally feel they pushed back the date of the release of this single and the album due to the hope of being able to perform in front of audiences. Otherwise I don't remember them having to release so much content with very small intervals. I mean they released Japanese single (OST), English single, Japanese album and a korean album in less than 3 months time with almost 3 months of no activities before that. Since the situation didn't get any better they have decided to go ahead.
Oh that's a very good point about how they were probably waiting to hopefully be able to perform with their next release, and now that they can't are just rolling it all out and moving ahead! I can see that.