Gold and happiness are both limiting factors to wide liberty. Liberty cities don't generate the kind of gold to keep up with the extra workers/units/city maintenance needed to support them unless you come up with other sources. You can (inefficiently) translate gold into happiness pretty readily through any number of purchasing structures and city state luxuries, if you had infinite quantities. So, while happiness is a problem for liberty, gold is truly an issue there as well.
This is part of the reason early wide strats are dependent on religion, which can give more gold and happiness than you'd get otherwise including some respectable per-city stuff.