In Western society women are regarded as the social and moral standard, so I think most men see either being married or at the very least being in a LTR as essential because it's an important form of social proof for a man.

An example would be in the UK at least it can be very difficult to rent an apartment or house as a single man, single men are assumed to be troublemakers and unknown quantities, so most landlords would rather rent to a single woman, a couple or a family.

Most single men in the UK tend to end up in bedsit accommodation, which is basically a single room in a shared house with shared kitchen and bathroom facilities because that's the only type of landlords who will rent to single men.

The only exception to this is single men with good jobs, like working for big corporations, banks, etc, but that's not most men these days.

Basically single men are seen as being at the bottom of society and most men see marrying or being in a LTR as the only way to raise their status.