Teams make strategy decisions on the basis of the regulations. Chucking the regulations out part way through a race is not acceptable
It’s simply that.
Merc would have banked on the regulation procedure, which is what we normally see unless overtaking is deemed unsafe (which surely wasn’t the case here).
Not only did the race director fail, it seems, to follow the procedure once (five of) the lapped cars were released, but he also chose not to release the cars behind Max.
That’s a clear and huge advantage to Max: free pit stop, fresh tyres, no-one on his tail, and Mercedes and Hamilton having no strategic option to defend.
It was as guaranteed a race win for Verstappen as ensuing under SC would have been for Hamilton. The difference is that ending under SC would have been an unexciting conclusion by the book, whereas this was a box office finish achieved by way of dubious intervention.