Because they are likely not living like that by choice. So, when they have the resources to consume more (which will certainly happen), energy-efficient choices need to be available.
Energy-efficient choices will make the same impact no matter where they're deployed. Arguably they'll have more impact in Western countries since they already emit more carbon.
"India (or China) has to do <something>" is bullshit. Everyone has to do go lower carbon right now. Richer countries can afford more expensive technologies today so they should go first. By doing so they'll drive down the cost for everyone else.