first of all, this is an english name, so who do you think are the poteitial stakeholders. Guangzhou is not easy to spell, write and pronounce in english. Would you name you son or daughter a name that nobody can even pronounce properly, let alone remembering it.
secondlly, "Canton" is a long long time-tested name to represent the city, almost as long as that of "China". so if you have no problem to the word "China" then it shouldn't be a problem for you to accept the word "Canton" neither . ohterwise, why don't you just rename "China" as "Zhongguo".
thirdly, it is all about advertisement. just as i said, most of the outsiders know "Canton", it service as a long term brand of the city. many cities are putting huge amount of money to promote their cities' prestige by doing advertisment around the world. Just for one propse: to know and remember my name, the same way as what a company does for their commercial products. so don't you think it is ridiculous to change the name from "Canton" to "Guangzhou".
and one more thing, not related to this issue. to answer you question about "why should we live for foreigners ?", if you don't mind, i want to expand the last word a little bit to "Others"
it is because no one will care about what you want, all the concern are what they want. so if you want to achieve you own goal, fulfill thiers first.