Normally when node peers communicate with each other, they will agree on blockchain fees periodically. What can happen is that if the last time the blockchain fees where agreed is when the blockchain fees were high. Then let's assume (because it was a force close anyway!) that one of the parties became unresponsive and then the force close will happen with the agreed high blockchain fee.

As per the "RBF", this is tricky because replace-by-fee creates a new transaction id and this new transaction fee may be unknown to the lightning node(s) in question.

LND handles bump fee with "child pays for parent" so that the original funding transaction goes through no matter what. If you were to bump a funding transaction with RBF then your channel will not get opened at least by your counterparty because they are looking for the original funding transaction to go through. For close it's surely the same, now for Force Close, I agree, it could just RBF but that's all really above my pay grade here :-)

The new Core 28 comes with nice improvements for these cases https://bitcoinops.org/en/bitcoin-core-28-wallet-integration-guide/

After a sufficient number of nodes upgrade on the network, the LN protocol may be updated to drop the “update_fee” message, which has been a source of unnecessary force closes during fee spikes for years now. With removal of this protocol message, commitment transactions could be set to a static 1 sat/vbyte feerate. With TRUC transactions, we can ensure that competing commitment transactions with anchor spends are allowed to RBF each other over the network, and if there are competing output spends from the same commitment transaction, that RBF can occur no matter which output is being spent. TRUC transactions are also allowed to be 0-fee, allowing reduction in spec complexity. With TRUC’s sibling eviction, we can also drop the 1 block CSV locktimes, since we are no longer overly concerned with what unconfirmed outputs are being spent, as long as each party can spend a single output themselves

I remember I closed a channel I had had open with a 'large' node... it wasn't a 'force close' just a regular close. And it went out at something like 80 sats/vbyte.

I don't know why it went out at such a high fee-rate... I certainly didn't select a high rate just the going rate at the time maybe a little higher. It wasn't a 'big deal' the channel had been great and had always worked. However I wish there were more transparency (?) why it closed at such a fee rate.

I believe that the value of the channel for as long as I used it far exceeded the opening and closing cost... however minimizing opening and closing costs is a good thing too.