The dynatoi have been cowed for decades precisely because of the Gardener's handiwork; he made examples of his enemies, he dealt with potential threats before they could truly take roots and become something more serious. Andronikos, on the other hand, has been doing the exact opposite; he's been propping up a façade of him being an Emperor who cares about the people, but nothing more; the work of his daggers remains largely unknown to both the dynatoi and the public, which is both good and bad. The people love him, and the dynatoi see him as as a man who wields power, but they do not fear him. The Sack of Barcelona, the single act that could've kept his vassals in check for decades if he used it properly, he foolishly attributed to his step-father in order to bring him down.
Poison keeps men in line, as Manuel said. And lets not forget that the dynatoi filling their coffers with German gold is something Andronikos brought onto himself fully; he did not have to summon Alexandros, he had armies in the Balkans that were just as large as the Persian host. But in the zenith of his arrogance, he greatly underestimated his cousin's capability, being certain he would fail. Had he done the right thing then, it would be him having this triumph, and being admired by the entire Empire. Had he realized what victory in France truly meant, he would've had the Oikoi follow the Makrinokomnenos the minute he left Konstantinopolis with his orders for the West. He would've had them ready to strike him down the minute he achieved victory, and he would've prepared a suitable puppet for the last remaining Exarchate.
Poison keeps men in line, as Manuel said. And lets not forget that the dynatoi filling their coffers with German gold is something Andronikos brought onto himself fully; he did not have to summon Alexandros, he had armies in the Balkans that were just as large as the Persian host. But in the zenith of his arrogance, he greatly underestimated his cousin's capability, being certain he would fail. Had he done the right thing then, it would be him having this triumph, and being admired by the entire Empire. Had he realized what victory in France truly meant, he would've had the Oikoi follow the Makrinokomnenos the minute he left Konstantinopolis with his orders for the West. He would've had them ready to strike him down the minute he achieved victory, and he would've prepared a suitable puppet for the last remaining Exarchate.