Utilitarianism makes a carrier believe that they should act to maximize social welfare and that more people believing utilitarianism would help toward that goal, so carriers think they should try to propagate the meme. Also, many egoists may believe that utilitarians would be more willing to contribute to the production of public goods, which they can free ride upon, so they would tend to not argue publicly against utilitarianism, which further contributes to its propagation.

My hypothesis seems a teensy bit different:

• Utilitarianism is a means of signalling what an unselfish goody-two-shoes you are - and many like to send that signal, even if they don't walk the walk. Utilitarianism seems to have hooked some moral philosophers - whoso job descripiton required them to send that message.

• Also, utilitarianism is a tool used by charities and causes to manipulate people into giving away their worldly goods. So: there are some financial forces that lead to its marketing and promotion.

I am sceptical about your story about egoists regarding utilitarians positively. Give me an egoist any day. The utilitarian is probably lying to others and to themselves, battling their nature and experiencing inner conflict. Their brain has been hijacked by a sterilising meme. At any moment, I don't know if thier utilitarian side will be dominant, or whether their natural programming will be. That makes it hard for me to model and deal with them.