I think nowadays there's the internet/phones/general technology which ruins relationships. For example, back in the days where there weren't any mobile phones, my mum and dad didn't speak to each other for about 4 days in between seeing each other. They saw each other on a Monday, didn't speak until my dad came over again on Friday or Saturday or something. I think it was a lot simpler back then.
Now, people expect good morning texts and “he replied with k, what does that mean?“ or “his ex commented on his status on Facebook, what does that mean?“ or something over the top. Even I sometimes get a bit silly thinking “I haven’t got a text from him the whole day, why doesn't he miss me?“ when in actual fact, you don't need to speak to someone every day, it’s just the way that our 21st century lives are going that its expected.
Also, I don't think people were as promiscuous back then as they are now. I'm not sure if sex is something that makes relationships difficult in some circumstances, such as you have played your best hand, there's nothing else to give, but I think that's another thread. It was more common to wait for marriage back then, whereas now, people start stressing that they haven't got any in two months.
With regards to online dating, it really is about the persons image, I know enough guys who have tried to start a conversation with a girl, and they just get ignored or "sorry I'm not interested" purely because of their looks! If someone likes your picture, then they will reply back, and it's an awful way to judge someone, but then I guess you meet new people online that you probably wouldn't have done in real life.