Yup. It does have to be spelled out in my book.
I get Secret Wars and all that inconsistent deus ex machine stuff.
Doesn't explain anything.
We just assume all those Sakaarian never died years before Secret Wars reset everything?
If Sakaar WAS rebooted, why do they remember the Hulk?
Did Hiro-Kala's story - linked to the planet's destruction - not take place?
To me this is a mess that requires more thought than just 'nothing to see here'.
The Marvel Universe has been rebooted several times already. Of the top of my head, I can think three: Chaos War, the 5 issue Defenders mini series, and PAD's 2nd Captain Marvel series. I'm sure there are more. It's not like Secret Wars has a monopoly on rebooting the universe.
There really should be an in-story explanation as to why an entire planet has been revived.