Thank you very much
The reason is that the Pixies got nerfed quite a bit.
They were really over powered and still are very powerful.
Take the Baphomet Pretender with F9S9 and 10 Pixies will rip through most Indies.
So by having them only have 10 Magic leadership it will be at least more costly in terms of gold and in lost research to expand.
Plus I think it's not really Pixie like to have large armies of Pixies.
Later in the game with a little more experience they can command 15 Pixies and the Ents can command some too. But if you really need a lot of magical leadership it's possible for Red Wood to cast "Awake Sleeper".