Answer:
Simply because tax-deferred accounts are taxed only when the investor receives or withdraws money from them. For example, a 401 (K)'s interest and capital gains are not taxed until the beneficiary retires and starts to receive payments, and that may take a long time.
It is not the same to be taxed immediately, because that reduces the amount invested. For example, you invest have $100 to invest and your income tax rate is 22%.