That is because these commands only work on trade/idle and partially jailbreak server.
That can be seen on the donation page too.
Idle and Trade Server Benefits
/dark - Turn black
/speed - Scout speed
/gimme - Give yourself any non-Valve weapon. [Instructions] [Weapons]
Increased Jarate ammo
Increased Sandman ammo
All of our quickplay servers have certain commands disabled. If you had speed on you, it would make the game unfair to the other players.
But these commands should work on 2Fort, except those marked with a *:
All Server Benefits
Connect when servers are full. [Instructions]
/hat* - Choose any unusual hat effect and color. [Instructions]
/saxxy* - Equip the Saxxy. People killed turn into gold statues.
/glow - A unique special effect
/swap - Change teams
/dsay - Chat with green text
/trail - Animated trails
AFK longer before kicked.
No advertisements between rounds
End of round (Humiliation) immunity
Autobalance immunity**
Faster cooldowns for using the /votemenu command
* Not available on quickplay servers due to Valve banning them.
** Balance is when 1 team has more players than the other. This is not scrambling which happens at the beginning of the round to make teams equal in skill. You may still be balanced if everyone else has immunity, which is very unlikely.