Tumbling only works if you're a small fraction of the total. If you put $300 million into a tumbler that only has $1 million of other volume, then it's pretty easy to track you.
Sure, but you don't tumble it all at once. Other commenters showed that these BTC were split up into ~1000 BTC chunks. Each of those could send randomly to different tumblers and anonymize all of their activities to send to a new set of addresses which people aren't tracking, and then from there gradually pull it out of various exchanges to various banks and accounts.
Sure, but if you have access to $300 million and want to tumble $1 million, wouldn't it be hard to track you?