In Texas it is the law.  Someone must be ultimately responsible for an agents actions.

Rightly or wrongly, it's law - plus they have good insurance :)

It's a legal requirement here. If you aren't a licensed broker, you must affiliate with one

Don't question authority, Just accept it and march on.

Because the broker knows what he's doing and you are clueless.

REALTORS® are different than agents and that is law in Oklahoma.

In Colorado, after two years of experience, licensed agents can work on their own as independent agents. It's not a bad system and there haven't been many problems associated directly with that.

They don't need to be if they have a broker's license.

It's the law.

because they can't sell real estate with just a sales license. They are licensed to work under a broker who is ultimately responsible for their actions.

A managing broker has the ultimate responsibility of the transactions of their firm.  It is a different licensing required by the state (managing broker vs. broker). 

Florida law.

Richard Weeks  nailed it. Not only in Texas. It the law in Indiana too.

It is like mentoring for 2 years.

If there's a "must" it's likely driven by law. So then, you must follow the law.

We're all brokers here in CO, but our first two years at least we're associate brokers and we do have to hang our license with an employing broker. They become responsible for our actions for as long as we remain associated.

"Must" aside, it does have benefits for all parties.

For them, it's taking on risk in return for some share of our income.

For us, it's having oversight, better insurance than we might be willing to pay for on our own, and hopefully, access to quality training, mentors, guidance, and gleaning knowledge from others. 

For the public - I think others have covered that well enough. :0)

The comments have already provided the correct answer - it is designed to protect the public and have someone responsible for an agent's actions.

Timothy Larsen The principal broker is responsible for the agent's actions and it is the law.

It is the law in Pa.

The buck has to stop someowhere. Brokers buy that buck

Because otherwise they would be breaking the law!

Someone has to hold your license.

Hey, this guy is from the UTAH RE School ........

The law.

It's the LAW intended to protect the consumer and hold 'someone' accountable.

However, that tradition is a porous as a screen door. Have a good understanding of your business plan, accessibility to your intended market that determine if YOU want to be a broker, join a tradition or take a look at what early implementers are doing.

It's the law in California.  

If you're not a full broker you must work under the supervision of one.

Someone needs to take care of the adminstrative responsibilities.

More to blame when the agent messes up.  The agent and the person responsible to train and manage them.  

to protect the public

Timothy Larsen - its a business model. An agent does not want liability of a broker, I guess.

We are in a very importatant business and I don't think very many agents right out of school have enough knowledge to not make major mistakes

Richard Weeks stated it well.  Someone has to be responsible for our actions.

It is important to have a broker you can turn to with questions or potential problems.

Some one needs to be responsible for all the people they give licenses to. 

Because when you screw up, they want to turn over the deepest pockets available.

Why car sales persons can not sell cars or cemetery plot sales person need to hang their license under a broker?