Nice analysis and good sequel of the post; I might include "read edjes.s comments for more info" in my posts ;)
If we are to say that there is something as perfect match, that is reserved only for the time of being in love, relatively short time at the beginning of the relationship. If we put aside disappointments after realizing that other person is not as we imagined it (idealized it) and assume that we are really perfect match, what will spoil that feeling is time. Everything that lasts changes and after some time our "perfect" relationship does not feel like that. Eventually, everything becomes boring, even most exciting thing, even if the thing itself did not change.
I will not go through the reasons why our cultures prefer single partnership but focus on the individual. From bio-psy point of view we can say that humans are not made for this or that but irl we see that they are, meaning, using our consciousness and will we can decide to try to overcome some characteristics biologically given or adopted during life.
As you said, modern way of life and development of tech had bid influence on relationships. One is that ppl are lately not willing to devote to themselves (so many escapist activities), let alone to someone else; ppl became spoiled, want everything here, now and without effort, without frustrations; want someone to make effort for them but when it comes to investing themselves in other person find it frustrating and too difficult. Adults started behaving more like children :) which is sign of emotional and social immaturity, sometimes serious impairment. Also important thing of this kinds of behavior is choice paradox, which is topic for itself, one of many on my list, waiting to be written, aside with influence of AI :)