I definitely see upsides and downsides to both. I can understand not wanting to tie all your money up in the housing market - millennials came of age during the housing crash and fallout, and are wary. Mobility and lack of responsibility for repairs and upkeep is great too. On the other hand, the uncertainty of renting really sucks (the LL could raise the rent, decide they want to sell, tell you to leave for other reasons), and if you want to "nest", it can be frustrating to not be able to do what you want to the house. Financially, it's hard to know which is better - housing appreciation isn't a sure thing, but neither is investing in the stock market.
After weighing these factors, we ultimately bought - but I could certainly see how people could come out another way.