It's actually very strange that Toei never adapted the Law or Ace novels into anime specials. You would figure they would be popular picks ripe for cashing in. The story is already written, the character designs are mostly out there, the setting is nothing special. Easy money, right?
Every year they do a special in late summer/autumn, last year they opted for the cheapest and easiest thing they could to celebrate the 20th anniversary: they readapted Romance Dawn but shortened it to 20 minutes. Below average a standard Wano episode in quality.
All I can really guess is two things: 1) Stampede took up all their resources in 2019. But they still didn't adapt novels in 2018. Film Gold apparently left them with enough time and money to do the Heart of Gold special promoting the movie. 2) Toei is pulling out of the anime special game. Maybe the business model isn't working anymore. Maybe their focus is Wano or other anime under their belt.
:sabogood: Happy to hear Boichi is at it once again. Dude has has his own manga but works tirelessly to keep promoting One Piece. He's a legit OP super fan at this point.