Not all the time the underdog loses the game but less chance of winning which makes a better choice for the favorite team.
If they don't lose often, then that means they are winning often, and that makes them a better choice in the game. It's just that there are times that they will get dumped by their opponents.
Usually, we take a look at their ratings and overall season performance and those teams we see that have higher ratings versus their opponents also have higher chances of winning.
This is true and we do this before betting. Maybe some will stick on these principles no matter what and there might be some who will pick the opposing team if the odds change.
Just having a quick glance, we know already where we put our bets. Sports is certainly not about luck but it is the skills and team participation, a way for them to win the game and their stats show who they are as a team and how they compete with others.
You just said that sports are about skills and not luck, so therefore a quick glance may not be enough to judge if who can possibly win but it needs a deep analyzation and research first. Teams doesn't know us, so it's impossible for them to participate with us and make us win at all times.