In the Bundesliga almost every season we see several teams competing for the title at the beginning of the season. But in the end the teams cannot survive in the competition. Last season we saw Union Berlin at the top of the table for a long time. Besides, the Dortmund team also tried till the end of the season to win the title. However, at the end of the season, we saw the Bayern Munich team become champions.
Leverkusen, Stuttgart, Dortmund and Leipzig are doing very well this season. But I have considerable doubts about whether the parties will be able to maintain consistency. It is very difficult for these groups to maintain consistency. But I guess the Leverkusen team will fight hard for the title this year with Bayern Munich.
Your observations is not perculiar to just the German bundesliga as the same can be seen in other leagues to such as the french Ligue 1, premier league etc, scenerios where teams will get to the top of the standings at the very beginning of the season and they sometimes put up very brilliant performances that will make you build some level of faith in them as to trusting them to win the league title but sadly they mostly end up otherwise.
Sustainability is the greatest challenge most of these teams face that causes them to drop on the long brun and never get to cling to the league title after staying at the top of the standing for almost half of the season, been able to sustain that position enough to end up winners is something most of these teams should work on and hopefully they will turn out winners subsequently.
Leverkusen is one team in the bundesliga this season that has shown a good level of resilience and readiness to be the winners of the league title this season, this is evident in their approach to games and how they win, they also seem to have some Level of sustainability to keep them going as they do not allow the team drop too many point enough to affect their position on the standing, I don't think they have gone below fourth position since the league started, hopefully if they can maintain this energy till the season ends they could beat Bayern to become the winners.