There are football supporters who can tell, within ten minutes, that their team is going to have a miserable afternoon. 
They have simply seen this version of the team before. The centre-forward keeps dropping too deep, the left side is getting crowded, and the opponent has worked out where the easy pass is. That kind of recognition is difficult to pick up on Saturday morning. It comes from watching the same sport often enough that certain details stop needing an explanation.
Different sports reward different kinds of knowledge
A tennis match can turn on something as mundane as where the returner stands. Move two steps forward and suddenly the second serve is under pressure. Move back and the server gets more room to begin the point. The scoreboard will keep reporting 15-30 and 30-30 while that small adjustment is changing the match underneath it. Horse racing has completely different clues. Watch the first few hundred metres rather than waiting for the finish and there is already plenty going on. One horse refuses to settle. Another gets the position its jockey wanted without having to work for it. A runner that usually likes to come from behind may find itself in a race with almost no early pace at all. None of these details transfer particularly well from one sport to another. That is the point. Knowing football does not make cricket obvious. Knowing racing does not suddenly make an NBA total easy to read. The sports betting menu puts everything close together, but the knowledge behind each market has been built in completely different places.
You also start recognizing what is normal
A goalkeeper wasting time in the 25th minute means something different if you know that team normally plays quickly from the back. A tennis player taking a little longer between points may mean nothing, unless you have watched enough of that player to notice that it usually happens when the match is becoming uncomfortable. This is why the best information is not always a breaking news alert. Sometimes it is knowing that a manager nearly always changes one of his wide players around the hour mark. Or that a particular horse has looked uncomfortable at the same course twice before. Or that a basketball coach tends to leave a starter on the bench longer than expected after two early fouls. None of those facts decide a bet by themselves. They simply stop you arriving at the event completely cold.
Knowing a sport can also make betting less busy
There is a curious side effect to following one sport closely: plenty of markets become less tempting. A match that looked straightforward from the outside can look horribly awkward once you know both teams. A race with an obvious favourite becomes less appealing when the likely pace looks wrong for it. A tennis match between two familiar names may be one you have no interest in touching because their previous meetings have been chaotic for completely different reasons. That is not hesitation. It is recognition.
What you know before the bet
Sports betting is much easier to understand when the betting part is not the beginning. The useful knowledge was usually collected earlier, during matches that had nothing riding on them, while noticing how a player behaves, how a team reacts, or what tends to happen when a race develops a certain way. By the time the odds appear, quite a lot of the work may already have been done.
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