Even if a person has a Last Will and Testament, it won't necessarily have to be probated. Why? Because not all property needs to be probated.
Many people own their assets in joint names with their spouse, children, siblings and others. If an asset is owned jointly with "rights of survivorship," then it will pass automatically by operation of law to the surviving owner or owners, outside of probate.
Many people also own assets that are "payable on death" to one or more designated beneficiaries. These assets will pass automatically by operation of law to the designated beneficiaries, outside of probate.
Many people have Revocable Living Trusts and have taken the time to fund their assets into their trust. If an asset is owned by a Revocable Living Trust, then it will pass automatically by operation of law under the terms of the trust agreement, outside of probate.
Many people also buy life insurance to provide income replacement and a source for paying off debts when they die. Life insurance proceeds will pass automatically by operation of law to the designated beneficiaries of the policy, outside of probate.
Finally, many people invest in retirement accounts, such as 401(k)s, IRAs and annuities, to plan for their retirement. If the account owner dies before using up the entire account for their retirement needs, then the account will pass automatically by operation of law to the designated beneficiaries of the account, outside of probate.