

It’s cause he can’t dictate that. Tariffs are just income to pay bills, congress sets budgets and even they aren’t too happy with a budget that’s increased spending. So it’s even likely his increases to ICE DHS that he requested won’t make it through.
He could try to siphon money from elsewhere, but that’d just get caught up in the courts (and he’d probably loose as congress owns the purse).
That budget hasn’t been passed yet to my knowledge. Not to mention the president’s budget request never makes it through, as the house and senate always have their own priorities.