I got married because I love my DH and for all the romantic reasons that that brings, I know that might make some people heave though. I also wanted him to be my next of kin and me to be his, if I has a serious accident I wanted him to be saying if they could operate on me or not, not my mum. We didn't have any money/property at the time (we a bit) so that didn't come into it. Now 15 years later I still love him just as much and we have three children and I appreciate the rights marriage gives us both and our children.
I do understand though why some people don't like marriage though, be it just the word or the whole institution, that's fine. Make you own legal agreements, define your relationships how you like, but all parties must be in agreement (as I said signing something) and should not just fall into it by default. The law should not be expected to have to guess your intentions.
And BTW without any snipes at any unmarried on here, I'm sure your relationships are as committed as mine. But, cohabiting couples are far more likely to split than married couples, even when they have children. This could be seen that some of them at least do not want the rights and obligations being married brings.