The reason behind it. Advantages and disadvantages.
Edit:
Okay, I'm feeling awake now. Here we go!
Homeside always has an advantage, I don't know why but it always has.
The away team are used to different conditions, the atmosphere that they're used to changes the way they play. For example, if you studied on your bed and took a test, you would perform worse than if you studied in a similar environment to the test conditions. Sitting at a desk can make a difference as does a 12,000 person crowd compared to an 85,000 crowd. Even the lack of glamor can effect the moral of the away side.
Although one team has more valuable players, this doesn't directly relate to being so much better. People think the difference between a tier 1 player and a tier 4 player is the equivalent to an ant vs a bear and that is not the case. It's closer to variations of juggle cats. Another thing, think of a gold vs 1 months wages in food. The gold may cost more but that doesn't make it better.
The away team for some are made up of players that haven't even been playing 1 year together, I'm going to make the assumption that lower leagues can't afford to buy new players as regularly and have a few years of play time together. This is a big advantage, players that play well together are better than players who are good on their own but perform averagely.
The playstyle of different leagues can come as a shock to players who haven't had much experience in those before. Being 'superior' often makes the players play in a more lax style until they realise they were mistaken.
Combine all those plus a mediocre(before above is applied) performance and you will always have these sort of results. If I remember anything else I'll add it to
this post.
I didn't watch all the games but the substitute keeper had a huge part in the game. If it was Cech it may have been a different end score.
Edit2: I remembered another one to do with being complacent. Going into the match with the egos half the players have, knowing that their wages and monetary value is more than the whole teams would give the another disadvantage.
