Zanzan's first Victory
The nobles' economic consideration first and foremost was that Alexander might be lying to them.
They feared that Alexander would simply give them peanuts in return for their contribution, only a small, token amount simply as a front to justify this extortion.
Hence, there were people who felt that whatever the money they saved would be better.
Secondly, some considered that even if Alexander had the best of intentions, he might simply not be able to provide the economic benefits he was claiming to give, i.e.- he was overestimating his abilities.
Then came the political considerations.
The risk of switching allegiance need not be said.
Even if Alexander could give them everything he promised, it would do them no good if Ptolomy and his faction were defeated, and the turncoats were charged with treason by Amenheraft.
Then they would lose both the gold and the goods.