BIP39 mnemonic phrases replace considerations about how to store one private key, with considerations about how to store the seed to a series of private keys.
The idea is that the private keys are hard to remember, worse to write down, and prone to discovery when stored digitally, so the solution is that you can have a phrase of words that act as a seed to a hierarchical deterministic series of addresses.
It seems like this idea has been lost in translation as the phrase length of mnemonic phrases has increased from 12 words, to 24 words, with the "more secure than thou" using even longer words and phrases, and security minded companies alike promote writing down the mnemonic phrase, in multiple places.
or splitting the phrase, or putting an additional passphrase on top of the HD sequence, or using Shamir's secret key.....
all of which simply create more points of failure.
Ultimately: instead of one paper wallet compromising one private key, your paper phrase will compromise ALL of your private keys. OOPS. or you forget the secret key, or you lose a piece of the phrase, or you misspell it
At least we can be confident that the words themselves contain enough entropy to prevent guessing, RIGHT GUYS? RIGHT?
What are the pros, cons, limitations of BIP39, or at least my concerns. I have read the wiki and the github markdown on BIP39, and these do nothing to alleviate these concerns because these BIPs are a centralized process