The issue is that they gave people 4k/ton prices in the first place.
It's a common problem with how the devs implement things in this game. If it's common to find 4k prices and 85k prices to sell (which is what happened right after carriers were released), and then the devs take it away, people cry nerf. People don't like things taken away, even if they were just given to them a day ago.
If the minimum buy was something like 35k, and the maximum sell was 55k, right at the beginning, and never changed, you wouldn't have this problem.
It's similar with LTDs. 1.6 million sell stations were left in the game for so long, that when the devs "rebalanced" it to 800k, people got very upset. But if they started at 800k, and remained that way, people wouldn't have anything to complain about.
The "balancing" in this game swings to each possible extreme every time.
Things are either buffed to ridiculous extremes (the "egg," LTD sub-surface mining yielding 40-80 tons per rock and selling for 1.6 million per ton), or nerfed completely to the point of uselessness. Why not find a middle ground? Put some thought into proper balance, and make it so.
But as it stands, it seems like every time FDev makes some minor change, it apparently has some ridiculous side effect. I wouldn't be surprised if this patch accidentally makes Benitoite sell for 3 million a pop...and makes mining lasers cause damage to nearby pirate ships instead of asteroids.