why do millenials and z generation love bernie sanders?

Like most Democrats he is a Socialist, they don't actually know what Socialism is and does to a country, and he promises to give away a lot at the expense of the tax payers, they also don't seem to believe "they" will have to pay those taxes.

Government schools have been raising them to worship socialism..

Pew Poll "69% of under 30 Americans think Socialism (by name) is better than free market capitalism".

You're talking about generations that grew up with unparalleled economic privilege and affluence...a generation that never knew World War or global depression first hand or through their parents...

These generations accept that obesity is one of the major problems with Americans living in poverty and that it's perfectly normal for "underprivileged" youths to be wearing $1,000 worth of clothing and jewelry...

What's more, these generations were raised by an educational philosophy that put their feelings over the ability to think critically.... and affirmation over the value of challenge and adversity...

Raised with these "values" why would anyone NOT support a culture of comfortable dependence that lasted throughout one's adulthood?  How could one NOT be unaware of the costs that go along with that dependence?

Because they have not been indoctrinated to think that anything vaguely socialist is evil incarnate, with zero thought.

They are capable of looking at Europe and Scandinavia and thinking "Wow, those countries that have a good social structure, a social safety-net, high taxes for the rich and state-run healthcare, actually have a higher GDP per capita than America does."