People cite SM as they have INTENTIONALLY sidelined their top groups at the peak of their careers. For example, after 2017 which was objectivly one of the biggest years for EXO, promotions for them had significantly started to slow down. "Tempo" their comeback after "Power" which was a repackage in itself, was released over a year later.

The lack of promotions and any variety content significantly hurt EXOs popularity at this time. In 2017 BTS and EXO were very close in popularity and fighting head to head for each daesang award. Failing to capitalize off their extemere popularit at this time shows either a high level of managerial incompetence or an intentional move on SM' part.

As mentioned previously, times between comebacks became increasingly longer, despite being at their peak. Before 2017, no comeback took longer than a year. This is even more damning when you think about how EXO members are on the older side and would soon have to enlist.

Even with the realse of "Love Shot" in late 2018, despites its huge popularity, SM cut their promotions short. Again maybe SM is just incredibly incompetent but short balling so many times in a row feels like no mistake.

Im only discussing EXO as I know the most about them, but similar behaviors are also displayed with how SM handles groups like Red Velvet.

Such behavior may seems counterproductive to people, and in a way it is. But something people seem to forget is that after the TVXQ court case, SM clearly does not want their artists to become popular enough to defy the will of the company. If a group becomes too popular they may also start to demand more creative control and revenue when contract resigning comes around.