The elves can't marry normally, you need to find a soulmate, (by romancing someone i think) then you can marry them, and having children is different from humans, elves can't "naturally" have children, they need to fuse their souls together with their soulmate to create a new ones, we built a new system for this, to showcase this and restrict elves from having to many children, if you want to know more, do join our discord and check out some of our dev diaries

Probably super late to say this.. I managed to marry legolas off to another elf and to my surprise they did have a kid. I didn't notice for 20 years so that is irritating.. Only kid they had though.

Goes with the lore of LOTR I reckon. Elves don't marry easily and only have one spouse their whole life, and they have a limited amount of children. Like Arwen never had any lovers besides Aragorn, and when Elves do love someone, they will never pick anyone else. So when Aragorn died, Arwen died soon after.