Ignoring the whole million dollar "reward" in OP's question, I'm curious as to why you guys would?
Why would we not?
To me at least, it was kinda strange seeing the relative openness to converting to Islam.
... if, of course, the price is right.
Fair enough, it's not like there haven't been any financial incentives involved for people to convert to Islam before.
If you want to call "keeping your head on your shoulders" a "financial incentive," sure.
Generally speaking, Islam didn't spread because people were afraid of having their heads cut off. In fact, it took centuries for majorities of the population to accept Islam in Egypt, Iran, and the Indus Region. This isn't even to mention how Islamization happened in Southeast Asia, parts of Sub-Saharan Africa, and Central Asia. Forced conversion was the exception, not the norm, and moreover, forced conversion is prohibited in Islam anyway as laid out in Surah Baqarah Verse 256. Right and wrong are clear for any man to see.
The main reasons it took hold among the local people after military conquest are the beauty and simplicity of Islam, proselytization (which often was occurring before any military action), prestige, and economic incentives. And even with many themselves converting for personal or financial gain, their children would end up true believers.