Marriage doesn't matter to some people. For some, if they aren't religious or are a different religion from their partner, that side isn't relevant, and the contractual and legal protection angle can be organised in other ways (wills, trust declaration on property, joint savings, life insurance, pensions, all the rest of it).
Equally, it matters a lot to other people, for religious, cultural, romantic, financial, and security reasons, all of which are totally valid.
There's nothing wrong with it being unimportant, or very important, or important for religious but not financial reasons, or vice versa. None of these are "unreasonable" inherently.
The problem, though, is where partners feel differently about it. You want him to want to propose, get engaged, get excited about a wedding and being married, and that's not going to happen, because he doesn't want that.
The other side - wills, savings, property, life insurance, pensions - that is absolutely important where one of you has taken a financial hit for your joint children and family, and wanting that sorted isn't just reasonable, it's essential.