Non-reinforced concrete has to be built bigger, but can last a long time. The coliseum is still up - Hoover Dam will also probably last awhile. And that's without much maintenance.
Smaller non-reinforced structures are harder to build. You have to use the concrete to hold itself up which requires a larger structure.
So you're left with reinforcement. There are options for non-rusting rebar, and non-rusting coatings, but I believe they're expensive. Also, any nick or scratch in a coating ruins it. There's also unique and novel research for non-rebar reinforcement - again expensive.
Here in US most buildings are built to last X years. So long as the rebar lasts longer than X, they'll use rebar. Increase X via regulations, and the quality (and cost) of the buildings in that area increases. Otherwise the bidder with the lowest cost of materials is most competitive. Anyone know what it's like in China?