Eternals, Doctor Strange, and all of the Disney+ series all went into production in 2019...and all announced the same time they announced the Blade. Also can't forget Shang-Chi which was announced..and if my memory serves me correctly, they had just found the actor like a week prior. In 2019, in one of the interviews during or soon after the panel, they had no immediate plans for a 3rd Spidey film, but by mid-2020 it was on go.
Yeah I did.
Bottom line is they all went right into production or had something brewing immediately, but Blade is taking its time. The only other time I've seen something similar to this was with the Gambit movie.