Bottas has clearly upped his game this season, and yet... it's still not enough. Not entirely Bottas' fault, of course. But given the status of the manufacturers, Hamilton's biggest rival is still Bottas, and so his (Hamilton's) priorities need to be:

1. Don't have any DNFs
2. Don't use up more PUs than allocated

those two things are what could potentially hurt Hamilton with respect to Bottas, and given the state of Ferrari right now, I'm sure he's thinking about what happened in 2016, and what he can do that's under his control to avoid that scenario. That would include being careful to not thrash the power unit. There's no sense in using more peak engine modes than he needs to to take whatever points might reasonably be available in any situation. Managing might make for boring races, but it's Hamilton's best strategy given the circumstances.

Since the beginning of the hybrid era, Hamilton has averaged 1.4 DNFs per season, mostly due to PU failures. A PU-induced DNF would bring Bottas right back into contention; he's only 29 points back.