Why was Oliver sent away from the workhouse?

Oliver, an orphan, is sent to the public workhouse when he is nine years old (chapter 2). While there, he is horribly mistreated by the members of the board who have little compassion towards poor people:

The members of this board were very sage, deep, philosophical men; and when they came to turn their attention to the workhouse, they found out at once, what ordinary folks would never have discovered—the poor people liked it!

These board members decide to starve the poor people to encourage them to get out of the workhouse.

So, they established the rule, that all poor people should have the alternative . . . of being starved by a gradual process in the house . . . With this view, they contracted with the water-works to lay on an unlimited supply of water; and with a corn-factor to supply periodically small quantities of oatmeal; and issued three meals of thin gruel a day, with an onion twice a week, and half a roll of Sundays.

The orphaned children have few other options of places to live. Still, they are slowly starved by the board members to encourage them to leave. One day, Oliver and his companions grow exhausted of being hungry. They decide (by lots—that is, at random) who will ask the leadership for a great portion of food. Oliver is selected for the job. He humbly asks, "Please, sir, I want some more."
The leaders are astonished that he would dare to ask for more. In fact, the leaders say that this shows that he will eventually turn into a criminal and be hung:

"That boy will be hung," said the gentleman in the white waistcoat. "I know that boy will be hung."

Immediately, the board members try to find another placement for Oliver:

Oliver was ordered into instant confinement; and a bill was next morning pasted on the outside of the gate, offering a reward of five pounds to anybody who would take Oliver Twist off the hands of the parish. In other words, five pounds and Oliver Twist were offered to any man or woman who wanted an apprentice to any trade, business, or calling.

Oliver is sent away from the workhouse for daring to ask for more food, though many of the people living at the workhouse are starving to death.
https://www.bl.uk/romantics-and-victorians/articles/oliver-twist-and-the-workhouse

https://www.gutenberg.org/files/730/730-h/730-h.htm