Buying a home isn't universally difficult across the entire country. It's more that many millennials choose to start their careers in expensive metros like NY, SF, and LA because that is where the jobs are but where a median salary won't be enough for you to save the ~$200k cash to buy the median home in those areas in a reasonable amount of time. There are a lot of programs that allow you to put less than the traditional 20% down for a home (I believe I read a stat that only 55% or so of homes are bought with 20%+ down payment), but again the issue is that a seller is going to view you as less competitive if you offer < 20% and will have a harder time having your offer accepted if there are multiple offers.

Anyone who is hitting their late 20s/early 30s and living in SF, for example, knows how many "going away" parties you end up going to of friends who've been here a few years, married/thinking of kids, and planned their escape so they have a chance of buying a home in less expensive metro.