I wouldn't say there is "massive" hate towards this format. It's basically split into four groups;
1. Neutral fans - they are the biggest fans of this format, they basically get to watch the biggest clubs go at eachother for the final two months of the season (and with this format, the title race almost always comes down to the penultimate or final game)
2. Fans of the "Big Five" (Brugge, Anderlecht, Standard, Genk, Gent) - the general feeling among this group is that they like the playoff system, which I don't think is that surprising since they much rather see their team play in big games than face smaller clubs, but they hate the fact that when starting the playoffs their point totals get cut in half
3. Fans of the teams just outside of the "Big Five" - there's a couple of smaller clubs who are fighting to make the championship playoff as an underdog each year (Charleroi, Zulte Waregem etc.) they are big fans of this current format because it gives them something to fight for until the final matchday. Before there were playoffs these teams would just finish 7th or 8th and basically know their season was over by January/February because they weren't going to climb much higher in the standings.
4. Fans of the small teams - they mostly dislike the system, they know they'll never make the championship playoff and when the regular season's done they have to play the other small teams 10 more times in a playoff system where they have nothing to lose (or gain) also, literally nobody watches these playoffs, crowds are generally smaller as well, players aren't motivated anymore etc.
It's not much better when you go ask around between team presidents either though. Some of them (Genk, Gent) desperately want to keep the current format, Anderlecht wants a regular season only with 16 clubs, Brugge want a regular season with 20 clubs.. These teams have to vote on the format but everybody wants something else..