I think BlackRock and Michael Saylor are planning for the long term. So that they can buy more Bitcoin and sell it at a higher price. Now it's time to see when the time comes for them.
I really can't blame you with an headline like that.
BlackRock are not the true owner of the Bitcoins they are holding
They are custodians more like managers and are paid a fee for their service.
Strategy service Now revolves around owning Bitcoin
So if they start selling, they last losing credibility and Goodwill.
If they do sell, the likelihood of them selling to take profit is quite low.
You are correct as BlackRock is more of a custodian rather than an owner of the Bitcoin they hold. The reason is that they do not just act as a store, where you sell, rather it is more of a management like service, and asset manager towards your clients, so their choice in selling is to a great extent on the expectancy and preference of their clients and not just on gaining personal profit.
Supposing that BlackRock embarked on selling Bitcoin in large volumes, the implication to their reputation would be enormous. It might harm their credibility which is already very strong and would be more insulting in the event that it appears more as a speculative act. Hence, I do not believe that they would act like that without a proper reason. They are oriented more at stable long term management, and are not oriented at gaining fast money that can spoil their image.