More than 90% of criminal convictions are the result of pleas, not trials. Few people can come up with the sort of money needed to mount a serious defense to a criminal charge. And in some cases the state can take your money up front, so you definitely don't have the resources to mount a defense.
You're right - and the plea process is part and parcel of Western due process. You're still facing an accuser and know what crime you're being charged for. You have legal council - even if court appointed - helping you make the plea.
None of which apply under the "social credit" system.