The reasons I've heard why the Dali didn't have tugboats guiding it out to the open sea don't really make sense to me

Life is a compromise between costs now and benefits later. Has any other ship collided with this bridge in its fifty year life? If not those in charge might have reckoned that not requiring tugs was a cost reduction worth the risk.

Some risk must always be accepted or we will spend so much on mitigating that risk that we have no resources left to mitigate other risks. The question is always how to balance the risks and benefits when you have incomplete information. It's all very well to say after the fact that that such and such a practice should have been different but before the incident the risks might have reasonably been evaluated differently.

After all if you really want to make it safer then that bridge should have been torn down forty years ago because it was discovered that bridges of that general design were not as safe as those built in more recent decades. That was not done; presumably because no one clamoured for it to be done or if they did because the cost would have been too high.

That's all probably true. A long term lower cost solution might have been better protection for the bridge supports (depending on water depth).