The main reason people do this is because they have been raised in such a way as to believe that love conquers all and overcomes any obstacle, or at least makes up for anything lacking in the relationship.
Now, there are many reasons why I do not believe this to be true. But they can all be summed up in one: the love that people have for each other is not strong enough to withstand distance. If it was, then long distance relationships would work out more often and people would not think of them as doomed from the outset.
Another reason why people believe in the idea of love conquering all is because they have been taught to think that way. People are raised by their parents and society to expect that relationships will work out, so when they do not some deep down part of them feels betrayed.
This is why you get those few people who do not believe in love, because they have been hurt one too many times and are now afraid to trust. They think that the only way to avoid getting hurt is to shut down emotionally and never let anyone close.
But this is not true. The only way to avoid getting hurt is by avoiding relationships altogether, not shutting down emotionally. It’s the former that causes you to get hurt in the end, while the latter can actually bring you happiness and love.
So, I hope that in the future people will begin to rethink their relationships and not just assume love conquers all because they have been told it does. It is better to be alone than in a bad relationship.