Why interface speed of 10G (10000Mb/s) is not getting set on a '1/10-Gigabit Server Adapter' ?

Issue

• In lspci output, card is getting displayed as 1/10-Gigabit server adapter, but still the maximum speed that can be configured is 1G (1000mb/s). Why?
• Below is the ethtool output:

Settings for eth2:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Half 1000baseT/Full 
        Supports auto-negotiation: Yes
        Advertised link modes:  100baseT/Half 100baseT/Full 
                                1000baseT/Half 1000baseT/Full 
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 2
        Transceiver: external
        Auto-negotiation: off
        Supports Wake-on: g
        Wake-on: g
        Link detected: yes

• Setting a speed of 10000Mb/s fails with error.