This has been covered in a number of past threads, so you might want to do some searching.
But here’s a couple things to think about.
1) There’s almost no way the seller will get the 3% that would have gone to your agent. In most cases the listing agent gets the commission and isn’t likely to give much if any to you for not having an agent of your own.
2) You can always use a discount brokerage which will rebate some (not all) of the buyer’s agents commission back to you. (There are reasons for and against this, I’ll leave it to you to read up on it)
3) You should probably only try to go it alone if you are fairly knowledgeable about real estate transactions. It’s not rocket science, but you need to know how the process works and how to protect yourself and what to do if there are issues during escrow.
4) Depending on the price and details of the purchase, (is it an REO, short sale, or regular sale) using the listing agent as your agent might impact whether you get the house, or someone else does. But if you read various threads on this site, you’ll see this can cut both ways.
IMHO, bottom line to this is that it isn’t as simple as some make it out to be, (although it’s not impossible) there are definite issues and risks and it is not usually a benefit to the buyer to go without an agent.
To answer your last question: Because the realtors have a really good lock on the system, and there aren’t many good ways to get past it.
