I think it's less about relationship commitment/expectations and more about the destruction of community through competitive individualism based on the sales pitch for "pursuit of happiness" under the non-intentional blind faith in market-based satisfaction.

In other words, recent generations have been groomed to buy or fake a happy life until one magically shows up in their very small slice of ConsumerWorld. Seeking more romantic/life partners is actually a replacement for the support of a fully interdependent tribe with useful goals. Now, everyone unto themselves, expected to navigate contrived societal chaos alone until "magic and life happens".

A natural tribe is by necessity, polyamorous in actions.