As to the causation, of the feeling of meaningless, one may say, albeit in an oversimplifying way, that people have enough to live by but nothing to live for; they have the means but no meaning.

Ever more people today have the means to live,
but no meaning to live for.

We have nothing to live but life itself.

If You've Got Nothing Worth Dying For, You've Got Nothing Worth Living For

Until a person finds something to die for, he or she has nothing to live for.

There are people so poor that the only thing they have is money.

Worthless people live only to eat and drink; people of worth eat and drink only to live.

Man always gets less than he demands from life; and so little do they demand, that the less than little they get cannot save them.

As the struggle for survival has subsided, the question has emerged: survival for what? Ever more people have the means to live, but no meaning to live for.

Hope is paltry food for living.

There seemed nothing to do but live.

While some no other cause for life can give But a dull habitude to live.

Venture nothing, and life is less than it should be.

Nothing’s worth living for if there aren’t things you think are worth dying for.