The reason for this is regarding the inequality in the matter of the huge economic difference starting next season between the SHL and HockeyAllsvenskan (each SHL club will get 45M SEK, about 4.55M€ while each club in HockeyAllsvenskan will get 2.3M SEK, 232K€) from tv rights and sponsorship money.
Why this is a bigger problem is that the SHL and HockeyAllsvenskan have the same broadcaster (C More), where HockeyAllsvenskan stands for about 1/3 of the income and gets nothing compared to it. Also, each league negotiate their own tv rights instead of the Swedish hockey federation negotiating directly with the broadcaster. As an example, the Swedish football federation is in charge of broadcast negotiations (where C More also has the rights) for Allsvenskan and Superettan (Swe-2) and have decided to split the money 75/25.
They are also very unsatisfied with how the current promotion/relegation system works.
Read more about it here:
Klassiska lagen i uppror mot SHL – kan lämna Hockeyallsvenskan