Being careful not to sound patronising towards the poor in public is one of the most ironclad unstated rules of wealthy social groups in the West. Breaking it immediately reveals one to be a member of the outgroup ("gauche"/"nouveau riche"/"tasteless"/"a philistine"), which will cause other wealthy people to break ties for fear of being tarnished by association. Since relationships with other wealthy people are a cornerstone of becoming and remaining wealthy, there is a massive incentive not to do this.

I think the underlying reason is that being patronised is very antagonising, and the poor generally outnumber the rich, who must ultimately depend on them in a variety of ways.

Exactly, perfectly put. It becomes an ingroup code, with very little to do with the actual people that are being discussed.

But if people want to have a serious conversation, it’s intellectually dishonest to steer around topics in that way. That’s how you end up with clueless policies.