Why do I have to pay an attorney to get my driver’s license back when my case was dismissed?

You are mistaken. First of all, if the case was dismissed, you cannot even do an expungement. Secondly, the case in court is completely separate from the case with the DMV. Winning the court case rarely means anything to the DMV. Chance are you have not completed the California alcohol program, so the California DMV will suspend your license indefinitely, thereby preventing you from obtaining a license anywhere else.

Because you "have to go through this huge process to get my license back". If you think that you can represent yourself and go through the process without an attorney, then you are free to do so.

I would check with he court to make sure it was dismissed. If if was get a paper from the court and take it to the DMV. That should resolve the matter.

You are getting ripped by the lawyer. Expungement does not cure anything for the DUI as far as the DMV is concerned. Also you can not get an expungement on a case where there has been no conviction. You can do you own hearing with the DMV. A dismissal will not cut it ;you need an acquittal of a PC 5138.5 motion be granted to get the DUI removed from the DMV. I do not know if either of those things occurred in California. Oregon's laws re probably the same as those in California but take a shot at the hearing and see what happens.

Nothing in this world is free. Even when it is free for you someone has to pay for it. Take at look at the contract you signed with your attorney and you will see that you agreed to pay the money. Contracts are not based on your subjective notions of fairness; they are based on terms that are stated in the contract.