Bitcoin should not be kept in one wallet, because if a single wallet is hacked, all the bitcoins will be lost. But it is definitely wise to collect bitcoins in multiple wallets, you should notice and think that the more wallets the safer they carry. El Salvador is a long-term holder so they should definitely use more wallets, using 14 wallets they hold 6285 bitcoins.
In my opinion, they should use more wallets, because they are constantly collecting bitcoins so the more wallets they should use the safer they carry.
That's a nice idea by El Salvador, they're not only preparing for the future by reserving bitcoin but also thoughtful about securing it from possible threats, the quantum computing machine has posed a great threat of being powerful enough to break encrypted algorithms, although the bitcoin blockchain is said to be very strong and has not recorded any hack but we don't know how powerful this machine could be, or if it's true that it could break into any modern encryption, well it's a good step for El Salvador to split their holdings into different wallets since they're aware that the creators of the machine would target big holders in the future if it the claims are true so that's why they're preparing for a worst case scenario by splitting what they're hodling to different wallets although 14 is too much.