Bitcoin is designed to be owned by us and make us our own bank without any third party interference. If you use the holding service, it is no different than you depositing your money in the bank. In addition to sending bitcoin to holding services will make it impossible for you to sell or use your bitcoin while your bitcoin deposit period has not ended, better hold your bitcoin and you can use them whenever you want.
Then why so many people use hot wallets and exchanges for holding their bitcoin? Only sophisticated holders use cold wallets and be their own bank. Most of the people just don’t care