Historically, motivation was to spend “local” or “remote” promise anchor without introducing additional pin vectors. It had a lot of shortcuts, including lack of efficacy under hostile conditions, and even in the positive scenario still cost considerable VBYTES.
Regarding various fixed vectors and their historical importance, I do not think it will be much better than the BIP431 motivation section for Truc transactions: https://github.com/bitcoin/bips/blob/master/bip-0431.Mediawiki#Motative
In short, there are many fixed vectors that existed when the lightning network was first released. “Full RBF” was not adopted throughout the network at the time. There are also RBF fees fixed, package restrictions, lack of package relay, and package RBF lacking, so replacement is too expensive (and incentives are not compatible) or in certain conditions.
Since Bitcoin Core 28.0, most of this environment has been changed. https://bitcoincore.org/en/releases/28.0/
The planned update for “Zero-Fee Commitment” channel (https://github.com/lightnning/bolts/pull/1228) will be removed and removed, resulting in greater absence and causing a smaller transaction of VBYTE. There may be a single anchor output with a 0 value (or trimmed HTLC amount), and the person who receives the benefit allows the two representatives to spend freely without signing.