It may be number of issues, or it may be "loose" vs "tight" clustering, where one side's issues tend to be mutually reinforcing where another's tend to be all over the map. The example that comes to my mind is the loose coalitions of the radical left in the 70's and 80's, when there were radicalized pressure groups whose hot button issues were: racial equity, feminism, environmentalism, labor, immigration, and maybe a half dozen others. There was a lot of rhetoric about there being some quasi-mystical substratum linking all of them, but you always got the feeling that the members of one group really didn't care all that much about the issues of the others, they were just trying to hold a coalition together to raise all boats.
In contrast, the radical right of today seems to have tremendous overlap between many of their hot button issues: prayer in schools, anti-abortion, anti-gay rights, anti-feminism -- there really is a substratum and it is self-identified as fundamentalist Christian. The other hot buttons: free market, anti-affirmative action, militarism, anti-immigration, gun rights, are a looser cluster, and there's nothing inherently linking them with the tight cluster except historical and demographic accident.