There may be several reasons for the contiunances frankly. There are certainly plenty of factual and legal issues that need to be carefully considered by the defense attorney BEFORE any serious plea discussions are even contemplated. The prosecution has several issues with regard to proving their case beyond a reasonable doubt it would seem. The long discussion on this case by so many without inside information, only the State and or defense attorney(s) may have. I also suspect that the State of CA may not have yet provided full disclosure and discovery of their evidence against Washington yet. For example, do we even know for certain that the prosecution has possession of his phone. Do we know who, if anyone, may be an actual witness to any of the facts. Rules of evidence will vary somewhat from state to state but I am confident that California will have to prove, by some method, that Washington, himself personally, received the electronic message (video) and also that he, personally, sent it. Just suspecting it doesn't prove it and it is unlikely that simply proving it came from the phone number assigned to 'his' phone doesn't prove he is the one who used it.
There also was some report that perhaps it was the girl's Mother who actually found the video on her phone and that is what started the mess. In such a case, perhaps the State cannot prove he sent the porn to a minor (if that is any element of the offense). There are certainly issues that must be investigated. At this point we have not seen ANY actual evidence of any crime - only allegations of such.
I suspect that Washington has not been presented with the evidence and witnesses against hiim and certainly has not had a chance to investigate or question the veracity of any of it yet.