I don’t think its fiscal conservatives specifically that are rare its small government conservatives that are rare. Small government and libertarian conservatives mostly exist as a significant force in America and even here they’re not that popular on the national stage. Outside its mostly big government social conservatives or moderates vs big government leftists.
The only complaints libertarians can have against social conservatives is they're not laser focused on lowering taxes and regulations, and they want to impose conservative social norms on left libertarians.
The big spenders in the conservative camp are national defense cheerleaders, neocons, and crony capitalist shills, which ironically include some libertarians.