This wasn't someone not being read their miranda rights in the back of a police car - it was a huge international operation that got a lot of press and attention.
Someone at the FBI probably got a verbal briefing from foreign agents about the US users and what they were engaged in and then decided that a dozen mid level drug suppliers wasn't worth yet another political fight over the 4th amendment, international coordination that effectively circumvents it and the legality of drugs themselves.
Remember, federal agents didn't get their shoot first ask questions later reputation from nowhere. Their bosses aren't blind to this. Each one of those fifteen doors you kick in comes with a non-zero risk that you create another Brianna Taylor or Vicky Weaver and in this day and age it might wind up in 1080p on Youtube before you can clamp down. What do you gain by this? Maybe you'll get a drug table photo op but it will be nothing like what CPB or the Coast Guard get when they bust a semi truck or a smuggling boat. You'll get to flaunt the fact that you took part in an international drug bust operation. But the public mostly doesn't care.
From the FBI's perspective the risk reward ratio of skirting the 4A to take part in this operation just just doesn't work out.