When someone is trying to avoid the mistake of using a single wallet like before when the wallet was compromised through hacking and the option of distributing his risks by having multiple wallets that are independent of each other is not safe in your view, which option is safe? At least you should have added a better option and not just condemn.
Also, having more seed phrases as a reason to believe the option is not good is baseless. If someone can keep a seed phrase for a single wallet well, I don't see how such can't keep it well for multiple wallets and it is not new for people to have more than one wallet without any compromise. We've been sharing enough ways to keep seed phrases on this forum, if you don't know, you ask.
If you are already confident that you can store your seed phrase well, why would you need to use multiple wallets to store your bitcoins?
This question is needless in my view as it doesn't have anything reasonable to add to the reason you asked it. What has the use of many wallets got to do with the safekeeping of the seed phrases when the person did not say the keeping is a problem? Are there many people having different wallets and keeping them very well without any compromise till today? If someone can keep the seed phrase securely for one wallet, why can't the person keep it for 5 wallets? It all has to do with your plan for the safekeeping.
Now, I need to hear from you, what is your plan for keeping your wallet that you are so afraid of using more than one wallet? You can't use your lack of safekeeping of seed phrases to judge others. Even if all my seed phrases are on a single sheet of paper it is often coded in such a way that you will not know the right combinations even if you had access to it. That's wisdom.