Typical corporate policy to reduce risk and exposure, likely imposed by a change in your company's risk management structure. I wouldn't worry too much about it. Consider being thankful that:

1. you can't be held resposible for anything happening after hours because you don't have access
2. the peace of mind knowing that you can't be called in to work after hours because you don't have access
3. access priveledges aren't a form of senority or tenure

As for your personal property being locked inside, you put it there. If you think you might need it, then take it with you when you leave each day. There is no law that says an employer must grant 24/7access to an employee's property left by the employee. Your only option is to contact your superior who does have access priveledges and ask if they can unlock the property for you to get what you need.