You asked me ''why SBS ?''
No. The 1st JG drama I ever saw was Iljimae, in June 2018 so I don't know exactly how much time he takes. As I know, JG is that kind of actor who immerse himself in the character so I suppose he needs at least 6 months to left it .
Then he needs time to study the new offers and decide which one fits him best. He is not a Copy-Paste actor or desperate for money...a drama (I'd also very much like a new movie...) a year is enough.
Now add to that Delight Asia Tour(the last Fan Meeting on 28 April in Seoul) and some events...so I'd say he is still in time