Because players/agents are not dumb. They know that, without interest, a dollar in 2060 is worth only a fraction of what it is worth today. And so when they negotiate, they can do a PV analysis like anyone else to compare offers.
It looks as though Ohtani did not sign anything close to a $700 million contract. He signed a $500 million contract, or something like that. Presumably, he is not stupid and knew this. And that is all the Dodgers should have to pay tax on.
I am as surprised today about how low this contract is as I was surprised yesterday how high it was. If it really is $300,000,000 deferred 40 years, it is worth far less than $700m.
Think of it this way. If the Blue Jays had offered $600m/10, no deferred, it would have been a better offer and Ohtani should have viewed it that way. Whether other factors were important, who knows?