Doyle did all right out of the arrangement. She rode a few winners (including a filly which gave her a few wins at Group 1 level) and no doubt earned some decent money.
The owner decided to have a change, which is entirely his prerogative. This situation has happened to plenty of other jockeys before Doyle and will happen again for as long as racing continues.
As an only occasional punter nowadays, I cannot get upset about a jockey losing their retainer. They only want to please trainers and owners, not punters.