Cisco ASA VLANs and Sub-Interfaces

Question:

Why I can not create sub-interfaces if I have the security plus license?
Maximum Physical Interfaces : 8 perpetual
VLANs : 20 DMZ Unrestricted
Dual ISPs : Enabled perpetual
VLAN Trunk Ports : 8 perpetual
Inside Hosts : Unlimited perpetual
Failover : Active/Standby perpetual
VPN-DES : Enabled perpetual
VPN-3DES-AES : Enabled perpetual
AnyConnect Premium Peers : 2 perpetual
AnyConnect Essentials : Disabled perpetual
Other VPN Peers : 25 perpetual
Total VPN Peers : 25 perpetual
Shared License : Disabled perpetual
AnyConnect for Mobile : Disabled perpetual
AnyConnect for Cisco VPN Phone : Disabled perpetual
Advanced Endpoint Assessment : Disabled perpetual
UC Phone Proxy Sessions : 2 perpetual
Total UC Proxy Sessions : 2 perpetual
Botnet Traffic Filter : Disabled perpetual
Intercompany Media Engine : Disabled perpetual

This platform has an ASA 5505 Security Plus license.
Please advise