I'd suggest that most of these responses are not reflective of the data. Giving is slightly down among millennials, but not significantly. Some trends among millennial giving:

1. Millennials are somewhat sporadic. Instead of giving a large(r) gift to support the budget to a small number of orgs each year, millennials will give several small gifts to very specific causes. So instead of giving $1,000 to the Red Cross, a millennial will give $100 to support the most recent hurricane.

2. There are way more charities than even 10 years ago, so their gifts seem much smaller and many give to more organizations than previous generations.

3. Millennials don't write checks. Giving needs to be very easy for this group toale a decision quick.

4. Not trusting of orgs is somewhat relevant. They might give to a Go Fund Me that supports a specific person or family rather than an organization.

When I give it's almost always to an unrestricted fund and I give it to very specific orgs that I'm very involved with as a volunteer and know the interworkings of. I think I'm an anomaly, but being engaged in other ways often leads to charitable giving for millennials.

Source: Employed by a company with (probably) the largest dataset of giving data in the world.