They haven’t shown that to be the case. I know many 30 something millennials with homes, kids and good jobs who are still solid liberals.
There are exceptions to every rule and I DO know quite a few Millennials who aren't anything at all like the majority of their generation...they are married, have at least one child, own their own homes, have good jobs, and are Conservatives. But sadly, they are the EXCEPTION and not anywhere even remotely close to the majority of that generation.