I've gaydar'd all dwarves in my fort. Out of 45 dwarves, only 14 can get married (and have, except two starting seveners who are lovers but don't seem to want to get married despite spending hours in the dating booth). Sexual orientation isn't the problem though, it's just that most dwarves are heterosexual (There's two bisexuals and two homosexuals), but they only have the 'likes (fe)males' tag, and not the 'will marry' tag.
Is there anything in the raws that I can alter next world to make dwarves just a bit prone to marrying?
yes.
in the dwarf creature definition file, you can throw in an ORIENTATION token to override the defaults.
In the bit where it defines the male caste, add tokens like:
[ORIENTATION:FEMALE:5:5:90][ORIENTATION:MALE:90:5:5]
And in the bit where it defines the female dwarf caste, add:
[ORIENTATION:MALE:5:5:90][ORIENTATION:FEMALE:90:5:5]
this will make a female dwarf for example, be 90% likely to want to marry a male dwarf, 5% likely to want a male lover but remain unmarried, 5% likely to be uninterested in male dwarfs, and 5% likely to want to marry a female dwarf, 5% likely to take a female lover, and 90% likely to be uninterested in female dwarfs.
The defaults are 75:20:5 for same sex, 5:20:75 for opposite, for the disinterested/likes/will marry. The numbers don't really matter, they don't have to add up to any particular value, but it's easier to use ones that add up to 100 for explanation purposes.
You can also try using DFHack to alter things in existing games, make them more likely to marry that way.