That time is completely configurable between you and the person you are opening a channel with, 3 days just seems to be the number everyone is gravitating toward using as a good default since it's long enough that short times offline won't cause you to be vulnerable to fraudulent transactions, but not long enough to cause issue if the channel you are working with decides to close up suddenly (because after the locktime is up you can broadcast a transaction which gives you all the money in the channel).

And yes, your bank can reimburse your for fraudulent charges (the amount and timing depends on your location), but that also depends on your bank not deciding that your fraud isn't actually fraud, it depends on you (as in your person) constantly checking your accounts for fraud and manually reporting it to the proper channels when it happens, you are still out the money while they investigate and reimburse in some cases, they will lock and reissue your card which often takes days to arrive leaving you without a card in the meantime, they can deny your account entirely for any number of reasons, they can control what you are able to buy with your card for any number of reasons, the cost of a bank account is far from free, they can and will charge you to get access to your own money quite often, and they can deny you from withdrawing your own money at any time for just about any reason (including "you are withdrawing too much money").

Neither option is perfect, nobody says they are, but I really believe that a system like Bitcoin and LN are a significant improvement over the traditional banking system in many ways. It is worse in some ways for sure, but I feel the benefits far outweigh the down sides.

> 3 days? In contrast, your liability is capped at $500 if you inform your bank of debit card fraud within 60 days.

Unless your bank considers the fraud to have been caused by a lack of care on your behalf, in which case you will not be refunded and have virtually no means of appeal

(note: Obviously depends on your country and local laws)