Combined they created a situation where there was absolutely no economic disincentive. It was "free" to attack the chain. Essentially the blockchain's survivial was based on "everyone in the whole world being nice".
It was not based on "everyone being nice", it was based on "not most people being crooks". If a sensible percentage of Eligius miners did not agree in being accomplices of such attack on innocent people, then he would probably have dropped it already. And if at least one other pool operator decided to counter his attack, honest miners could migrate from Eligius to this other pool and even if Luke-Jr decided to attack "no matter what", he would be outnumbered.
Anyway... it was definitely not "everyone has to be nice for it to work".