It’s quite simple: he tried to do things himself without engaging with a qualified solicitor first.
Apologies if I've missed it, but I can find no trace, prior to the hearing, of any forum expert advising the OP to engage a qualified solicitor, let alone of the OP ignoring this advice. We could all see that he was relying solely on this forum for "appropriate advice" on "how to do things himself".
But this advice turned out to be inadequate, as it didn't envisage the unexpected absence at the hearing of the prosecutor, with whom we'd all been advising the OP to engage. In the event, the OP having his own solicitor there might well have resulted in no £10 conviction, but a (more desirable for both parties) £365 settlement.
But this is all water under the bridge, as the OP has indicated that he (or perhaps she?) will probably have to accept this imperfect outcome.
To avoid a recurrence of this episode, can an Expert advise whether a Prosecutor is indeed obliged to attend such Hearings. And how should the defendant act in response to any such absence?